Would a RM250A (1976) motor do?
I have one I built when I first rebuilt my 250A/B (A motor in a B frame) four or five years ago. I since rebuilt another motor as a separate project that's in the bike now and has been for the last two or three years.
The original motor hasn't done too many hours since rebuild, 5-8 ride days perhaps. It was fully reconditioned with a Serco rebore, new Wiseco TS250 piston and rings, new genuine Suzuki seals, new bearings. No rotor, stator, mag cover or sprocket cover.
Asking $425 + postage/freight. Or if you're going to CD11, we can arrange pick up from there. I'm in Brisbane.