There's one in every Campagnolo tool kit. Almost every LBS who carried high end bicycles had one of these, as it was the cheapest method to get a complete set of facing, reaming and threading tools. Given that the OP lives in the Boston area, I imagine there are a few shops around that would have them.

As suggested by Michael Angelo, using a 10mmx 1mm die on the derailleur hanger bolt is another option, but tapping the dropout is preferable, as it is softer steel than the bolt.

Of course, it can always be just forced in, as you suggest. A lot of Campagnolo dropouts had Shimano bolts forced into them in the late 1980s, after SIS arrived. The derailleur bolt is not a high load situation where proper thread form is critical. Still, I wouldn't want to be switching back and between Italian and non-Italian derailleurs.