I had very good luck with a one-man shop named K's in Plainfield, NJ. The guy charged me $90 to boil, rod, and re-solder the radiator in my '29 (pictured) and did the job in a few days. That radiator came from the same NJ maker that LarryH mentioned above.

K's does a lot of such work in this area, and leaves the radiator on cars like mine unpainted so OEM paint can be used on restoration jobs, if desired. If you can, find a shop like this one, where the owner knows his or her stuff and his willing to treat custom cars as what they are. Since then, my cooling problems are gone, although it does puke coolant every now and then, so I'm going to fit an overflow tank.