It is entirely possible to build an M300/M600 weapon light without using a single Surefire part. Arisaka, who already makes an great M300/M600 body and mount, has now introduced their M300/M600/E-Series Tailcaps. These tailcaps feature a forward clickie switch with a fence to prevent inadvertent activation. Most importantly, the tailcaps are built around the proven McClicky internals.
Check out the M300/M600/E-Series Tailcaps from Arisaka.