Some were converted to 7.62x51. They however command a premium of $400-$500 range. Regular ones are anywhere from $250-350. All in "near-unissued condition, slight scuffs and scratches"
I'm skeptical of conversions. I saw a CETME that had been converted from .303 to 7.62x51 and I'm glad I didn't get it. I read later that you're liable to wind up picking the chamber out of your face with tweezers. I don't know the first thing about the 7.5x54 to even be able to speculate.
Weird, I thought the OP made this thread for the soul purpose of taking a shot at the French (which I am more than fine with). Turns out he was serious.
Take an actual shot. These French MAS rifles (bolt action or semi-auto) are all good, sturdy, acurate guns. Though I own original calibur (7.5x54mm MAS) examples only.
I used to have one that was converted to 7.62x51. I never had a single problem with it. I probably put 500 rounds through it. I have read that some of the conversions were terrible. I guess I got lucky.
Mine jams after it gets warmed up. I did find a really good article on what the real deal is on fixing these (actually two articles) but this one was much more explicit in the fix (gas timing).