Try batteries plus http://www.batteriesplus.com/
Most of the drill battery chargers, especially the multi-volt ones, will have a full 120v at the contacts when plugged in, so it's not a very good idea to try and use alligator clips with one. They sense the charge by sensing the current going out, with no current they are just on.
What is keeping the battery from just plugging into a main brand charger? If there is a ridge or something, just cut it down so it fits.