Hi Joe.

A good source of used vacuum pumps is the graphic arts trade (i.e.
supplies for plate making and printing). Every print shop used to have
vacuum frames for holding copy flat and in position. All that traditional
equipment (large cameras, lights, frames (copy and contact), vacuum pumps)
got replaced by scanners. Yellow Pages should help you find a graphic arts
dealer in your area.

I also found some small vacuum pumps in an electronics/surplus store quite
a few years ago that came from dismantled scientific gear.

Hope this help! Regards.

Andypack