The reflector was from the xenon lamp module of an old Underwater Kinetics 2xAAA light.
It came pre-focused for spot mode with its xenon bulb. I sawed through the bottom of the plastic reflector with a hobby saw, rotating the reflector when I hit the bulb inside When I'd gone all the way around it, I pulled off the reflector and discarded the rest. Then I used a drill matched to the width of the XM-L emitter to widen the hole slightly. I used arctic alumina thermal epoxy to glue the reflector to the white plastic retaining ring that came with the SK58 and was originally used to hold in the metal washer around the emitter.
It looks like Underwater Kinetics still sells these lamp modules. I find they reflect considerably more light than the reflector from a 2xAAA maglite, which I've also tried.
http://www.uwkinetics.com/products/uk2aaa-xenon-mini-pocket-light
Note that I made no attempt to try to get the reflector to perfectly focus the emitter die. It really isn't necessary with this setup. My goal was to make a more beautiful flood mode while giving some usable spill in spot mode and that's what this setup gives.
