How precise do you need it?
If you just need it to be consistent then you could probably make one
faster than you could search for one.

How about a heating element (hot plate, toaster) and a digital t'stat?
I'd use the Ranco brand "ETC".  About -30 to +100'C, 15 A relay,
1 deg differential, 1 deg resolution digital display.  (Refrigeration
stores, about $45)

Joe Lepine