About finding parts, never had a problem finding anything for the 93 I have. Between all the wrecked GTs, ebay and salvage yards, no problems. Though the parts are a bit more expensive it seems unless you look around. But I haven't had to get a lot of parts either, so a lot depends on how well the car has been taken care of in the past.
I'd say don't let the 122k miles worry you as much as the typical signs of abuse, it's more about the maintenance and abuse than the miles I think. I got mine off a lot with 142k miles on it, now it's at 252k, and haven't spent a ton on it. My experience with the gt's has been fix a problem once & its stayed fixed, a honest mechanic helps tons, too.
YMMV, Good luck!