Looks like Lumens Factory still sells P60 type incan modules on their website. In the Category menu, go to Lamp Module, SureFire Compatible, D26 series. They are listed by voltage (4, 6, 9). The "4" is a 3.7 volt bulb for a single lithium ion battery.
I bought two of the EO4 modules years ago back when Lighthound was still in business and selling a bunch of Lumens Factory stuff.
By the way, I've heard that high-pressure gas bulbs such as P60s can be a real eye hazard when they pop, so put on some eye protection before messing with them, if anyone is thinking of trying to R&R the bulb itself.
( edit: Dang, I found the screenshot of my EO-4 purchase... it was in 2009! Hard to believe it was that far back. I did notice that the Lumens Factory site's price for the bulb is still the same as what I paid back then (14.99) so kudos to them! :thumbsup: )