nlerner, a C&V Forum regular, but I haven't seen him post lately, is from Brookline, and he had several frames powdercoated by a fellow in Plymouth, MA for about $75 per frame. The results were good.

Alternatively, hand sand the frame, remove the rust, and rattle-can spray it yourself. The tougher stuff recommended here has been engine block paints, brake caliper paints, and appliance epoxy paints. The latter seems to be favored here recently. Mask off the decals, gloss black is easy to find.