Hi roosika, any red led ultrafire 501b on ebay (make sure its single mode) i paid 8 pounds for mine, the lens is in the link on the thread (lens was 1.50 i think)
Its the best 5 min project ever lol. And for less than a tenner you have a great lamping torch! They are a million times better than the standard 501b. My shooting mates that have seen them have all made one and prefer them to there lamps!
You can get green too. Just replace the old flat lens for one of the curved dx ones and paint your reflecter black. (remove it from the bulb first.
Hope you make one, you will NOT be di