Supposedly LaserPointerStore is a decent source, but I haven't received my order yet so I can't say from personal experience.
Side note: make sure you know how to treat 18650 batteries safely, and get a pair of laser safety goggles. Once you get into higher powered lasers, even looking at the dot at close range can permanently damage your eyesight, and accidental direct eye exposure even at long range without proper protection can cause bleeding in the eye, scarring, or blindness.