How do i get to park lockout mechanism and where do i get replacement part?

The brake light switch also controls the shifter interlock mechanism. Check the switch

Define won't crank ? I'am assuming the key will turn to the start position ! When doing so does the starter spin the engine or not ? Trying to define your problem of won't crank . If when you turn the key to start position an the starter spins the engine over but doesn't start an run , this is a cranks no start condition . If nothing happens when you turn the key to start , this is a no crank no start condition . Your vehicle has a safety system , shift interlock , won't let it shift out of park if the brake pedal isn't pressed . Won't let the key turn off either . Electronics involved , locking solenoid's etc.... Floor or column shift ?
The automatic transmission shift lock control system is a safety device that prevents an inadvertent shift out of PARK when the engine is running. The driver must press the brake pedal before moving the shift lever out of the PARK position. The system consists of the following components:
• The automatic transmission shift lock solenoid (serviced as the automatic transmission shift lock actuator), as well as the body control module (BCM) and the engine control module (ECM)/powertrain control module (PCM). The shift lock solenoid is located within the floor shift control assembly with vehicles equipped with floor shift.
• The BCM controls the voltage supply circuit of the shift lock control solenoid. The following conditions must be before the BCM will supply voltage to the shift lock control solenoid.
The BCM controls the voltage to the shift lock control solenoid through the shift lock control solenoid controlled voltage circuit. The following conditions must be met before the BCM will supply voltage to the shift lock solenoid:
• The ignition is in the ON position.
• The ECM/PCM sends an input via GMLAN serial data to the BCM indicating the transmission is in the PARK position.
• The BCM determines the brake pedal is applied according the brake pedal position.
Since the shift lock control solenoid is permanently grounded, the BCM supplies voltage to the automatic transmission shift lock control solenoid, mechanically unlocking the shift lever allowing the driver to move the shift lever out of the PARK position as the solenoid energizes. When the brake pedal is not applied, the BCM turns the control voltage output of the shift lock control solenoid OFF, de-energizing the shift lock control solenoid. The de-energized solenoid mechanically locks the shift lever in the PARK position.
During remote start operation, the BCM will de-energize the shift lock control circuit, locking the shift lever in the PARK position.

Plus the reverse lock out !
The reverse lockout system is a safety feature which prevents an inadvertent shift into reverse at speeds above 5 km/h (3 mph). The system consists of the following components:
• The engine control module (ECM)/powertrain control module (PCM)
• The reverse lockout solenoid
With the ignition ON, battery voltage is supplied directly to reverse lockout solenoid. At forward speeds above 5 km/h (3 mph), the ECM/PCM commands the reverse lockout solenoid ON by grounding the control circuit of the solenoid. This energizes the solenoid and mechanically prevents the shift lever from being moved into the REVERSE position. At forward speeds below 5 km/h (3 mph), the ECM/PCM commands the reverse lockout solenoid OFF, de-energizing the solenoid, which allows the shift lever to move into the REVERSE position.

Power Mode Master
This vehicles BCM functions as the power mode master (PMM). The ignition switch is a low current switch with multiple discrete ignition switch signals to the PMM for determination the power mode that will be sent over the serial data circuits to the other modules that need this information, and so the PMM will activate relays and other direct outputs of the PMM as needed. Refer to Power Mode Description and Operation for a complete description of power mode functions.
You have no clue of the electronics in your vehicle , your best bet have it towed to the Buick dealer .

park lockout, is active. ( and is malfunctioning)
read the gove box opr. guild, see page on starting car
see page on how to by pass the park lockout feature .
do that until you fix the bad park lockout , circuits.

Either your not pressing the brake hard enough to activate the park lockout actuator. Or the park lockout actuator is bad or disconnected. It also could be the brake pedal switch is bad or disconnected. Just a guess, you did not specify what kind of car you have.
If you are able to physically move the shifter into park, but the car transmission does not go into drive then It could be several other problems: for example: low transmission fluid, clogged transmission filter, or the shifter cable is disconnected or too loose connecting to the transmission, or internal transmission problems.

The mechanism for the shift lockout button is probably jammed, you will need to disassemble the mechanism to clean/re-lubricate the affected parts.

Its the Shift Park Lockout mechanism. You can watch a video on you tube from Billets. They make a replacement part that is not as fragil as the plastic one from the factory.

There are few things that has to be checked 1)Transmission Lockout switch on the brake pedal 2) If transmission lockout switch checked out OK , then the solenoid on the gear lever that is activated by that switch has to be checked. 3)Step on the brake pedal and see if the brake lights come on. If they don't, check the brake light fuse to see if it is blown.
If the brake lights come on, then turn the key to where the steering wheel unlocks, but no lights come on. Set the park brake and see if the shifter will shift into neutral.
If the shifter moves out of park, then you will need to check the shift interlock actuator as its not getting power when the brake pedal is depressed. Thanks. you can rate this solution and show your appreciation.

This is a very common problem on the Chrysler LX Platform vehicles from 2005 - 2007. It's a broken Park Lock-Out Mechanism made from cheap plastic. Chrysler will only replace the whole shifter because they don't make just the part you need and it will cost you some bucks if you are out of warranty.

There is a way to over-ride the Lockout and you can purchase just the replacement piece from the only company that makes them in 100% aluminum billet.....BilletTechnology.com. Go to 300cforums.com or lxf.com and search for "pink thingy" or park lock-out mechanism. Tons of information as well as DIY threads with pictures and even YouTube demos.

in most cases the shift lockout mechanism has to see a signal from the brake light switch, poss. the brake light fuse is blown or the brake light switch is iether out of adjustment or shorted, first have some one stand behind the vehicle while you step on the brake pedal, do you have brake lights ? no, check all the fuses, and or brake light switch, yes, poss problem with lockout system.

If the transmission won't shift out of park, take your center console out around the shift lever, it's kind of annoying with it being in park. Then in front of the shifter you will see a little lockout solinoid unplug it, it will only have two wires on it, then follow it down to a little metal lever push the shift button and push down on the lever at the same time if it comes out of park turn your key on put it back in park while the lockout switch is still unplugged, and with the key on, it should come back out of park. If it works like this then your lockout switch is bad.