I just ran accross a pic last month of dad on the 250R.
Best i can remember, it was an 83, the motor was punched out to 327cc, ported, 44mm carb, Bills Pipe. i remeber seeing a piece of tape on the air box lid that said 270 main jet.
I would try Dennis Kirk for parts. They seem to have a lot of stuff.
Dad was 42 i think(13 years ago) when he bought it from my uncle. He didnt keep it more than a year due to the unpredictable powerband, and lack of low end. he traded it for a 350X.