Gunsmith question

What is the best way to get a choke that is seized up, out of a barrel?

Good soaking in Kroil or similar penetrating oil is a good start. I would put the barrel with choke down in a container filled enough to cover the choke and leave it overnight and then try it again

+1 on Kroil.

Kroil is my personal choice you have to order it though. A 50/50 mix of automatic transmission fluid and acetone or a similar thinner works better than most locally available break free oil.

Yes ^^^^^ Maybe heat it with a hair dryer.

Not sure what tube wrench you are using bit if it has "extended arms" use some sort of cheated bar.

THEN, clean all treads VERY well and use an anti size grease.....

Don't worry most of us have been there

Good soaking as already stated. If you're using a flat choke wrench there should be a hole in the top you can slide a skinny Phillips head screwdriver through, that'll give you some leverage, and a place to put a cheater pipe. Also, I know it sounds counter-intuitive, but you might try tightening it. Lots of times there's just crud in the threads and it's easier to tighten than loosen. Once the crud breaks loose it might back out OK. Best of luck with it.