I can't specifically recommend a place to search for a used Polaroid Slide
processor but be advised that there are two models. One is called Automatic
or something like that the other was sold as a "darkroom in a box" and is a
hand cranked model. Either will work but the automatic is motorized and
probably more convenient. The original hand operated model sold new for
around $100 and years ago could be had used for about half that...
As with all polaroid processors, backs, cameras, etc it is essential to keep
the rollers clean or you will suffer uneven development, spots, etc.
Have fun.
Hal