I suppose you could pick up a 3V boost driver from illumination supply or one of the Chinese vendors but at only .5A it will be pretty anemic compared to what you could do with a couple 3 x AA holders or some lithium cells. The LEDs are probably wired in series so you’re looking at needing 9-10V to get it working unless you rewire for parallel to get down to ~ 3.3V.
They should get ~2.8-4.2v, that’s what the vast majority of emitters used in flashlights run at (the exception being the 6V MT-G2). Brightness is controlled by current, not by voltage. I have no idea what emitters that uses, didn’t look but I know for a fact they run at ~3v.