The ones I see most with remote battery packs are those made for bicycling, you might browse that sub-forum.
My approach has been to find one that I can mod by tapping into the battery compartment with a harness lead. Target had a dandy one on clearance last spring with two side-by-side CR123's that would run great on one 18650 (or 2 parallel). Those were a Q-bin Cree XRE driven at around 700 mA, IIRC, so around what you are looking for. Unfortunately, that particular model is all gone, but you may be able to apply the concept to another.