Your best bet is either ebay or to find a unit for parts. I've got 3 RT-909 decks. 1 fully functional, 1 under construction, and 1 tucked away for parts since it would be work than what it's worth to fix it.
BTW, Pioneer still carries a couple of parts for it. Pinch rollers, belt, and heads are about the only thing left the last time I looked.