I asked this question a while back..... I personally would advise against the V71 holster, as it has metal springs that are hard on the finish of the light, and also, the M3 is a little long overall for this kind of holster to work best.
I have a Maxpedition universal baton/light holster, which adjusts the size by velcro for length and also diameter.. It's OK, but not perfect. I'm waiting for a BDS pouch designed for the M3 to arrive, but opinions on here vary as to it's build quality. The V40 pouch for the 9AX will fit the M3, even with a Z48 tailcap fitted.
The M3 is an odd shape, the grip ring tends to snag on soft pouches, and the body diameter is different to th egrip ring, so any pouch has to be wide enough for this.