To be honest Paul i think they're probably only the tip of the iceberg. Whereas Aligarh and Jodhpur are the most well known and established, these days it seems they are coming from all over.
There are a lot of countries still using very old techniques for working metals, so a lot of such workshops dotted all over the world.

Lost count a few years ago how many times you'd see antique padlocks on auction sites or online dealers for anything upto £500+ ,that were the exact padlocks being sold by online shops like scaramanga for 20 or 30 quid!