What you want to do is degauss the tube.
I do not believe a supplier will sell a CRT to anyone thats not a TV Tech. Safety/liability issues. The CRT is vacuum sealed and will implode
if broken and the tv has 25000 volts
even after unplugged for several days !!!
A CRT may cost as much as a new tv.
Several methods some people have found useful are;
Method (NOT soldering iron)
1. Hold the soldering gun to that the rear of the case is toward the screen (the tip is facing away from the screen at a 90 degree angle) A magnetic field is generated by the transformer in the handle.
2. Place the gun in the center of the screen and turn it on, keeping it near but not touching the screen (to prevent scratching)
3. Slowly move it to the top edge (or any edge), then slowly around the outer part of the screen (but still in front of the glass) until you return to the top (or the edge you moved out to), again slowly return the gun to the center of the screen.
4. Keeping the gun on, slowly pull it straight away from the crt
until there is no more distortion visible (usually 3-4 feet), then turn the gun off.
Rigged Drill Method ( parts can fly off so take care)
1. Get a magnet and tape it to the end of a high RPM drill and make sure it is held in place very tightly, use Duct or packing tape
2. Hold the rigged drill next to the spot to be fixed, make sure it is about 1-2 inches away from the screen
3. Now pull the trigger an you'll see the screen blur fast, this is normal so do not worry
4. Whilst the drill is running, slowly pull away from the screen and you may see it is fixed
5. This process may need to be repeated due to magnet strength and drill speed but it will work
6. Due to physics the fast, random turning of the magnet/s will fix the screen's colors