Where can you get new computers for C5's and will anything else work?

I have a 98 C5 a4. My computer got locked and im using a new tuner so a new computer would make it alot easier. I know fbody guys can get a new one at o'reilly's but I dont know if they have C5 computers. What do you have to match for a computer to work. Does it have to be a C5 computer, does it have to be the same year and does it have be the same tranny? Anything else you need to match up?