Nancy, seems to me you can find lots of places to find wholesale mason jars but to get them painted, which IMO is more likely to be done free-hand, they would come from an artisan who wouldn't be selling them wholesale.
I could be wrong....
If you have a college or even a jr college in your area, I would contact an rt teacher there. I am sure there are art students who would love to make a few bulks & get some paid art experienec to boot.
If that does not work, how about making contact with your town's local art league or association to find someone to paint your jars?