You would need to contact the manufacturer directly in most cases and even then they often do not want to sell them as stolen decks often do not come with a cable and they are trying to reduce theft.
It will depend on the capability of your amp. Each sub has dual voice coils (DVC). Each voice coil is (probably) 4 ohms. If your amp is a single channel, 1 ohm stable amp, you can connect all of the voice coils from both subs in parallel on the amp output. Other configurations will depend on the amp's number of channels and minimum resistance your amp can withstand.
