I wouldn't be too afraid to head to NAPA with my old one and cross it out to something they have. Couple cases in point - Few years back had an air-head Beemer (R100RS). Mechanical voltage regulator went bad, went to NAPA and crossed out one for a BMW auto, their Echlin brand. The replacement was digital/solid state, slightly smaller and had a pigtail hook-up rather than the plug being built-in. Otherwise it mounted to the same holes, plugged right in, and worked flawlessly till I got rid of the bike. Oh yeah, it cost a quarter of the BMW piece. Year and a half ago I got glow plugs from NAPA for my M4500 for less than a third the price they were going to cost at the local dealer, which is significant, cause it takes 6 of 'em.
Voltage regulators in general - don't forget that most mechanical units have to be polarized to work properly (esp on the older "generator" systems).