I picked up a 4006TSW today, and I plan to put a TLR-1 or Viridian X5L Gen3 on it. Does anyone know of a good OWB option for this combination? I’ve found a few holsters that just fit the gun, but nothing for gun + light.

I would check with holster makers that have been around a bit.
A 4006 that actually mounts a light is not terribly prevalent. Might be a challenge...
I looked at Ted Blocker (pancake) and AE Nelson (paddle) and they both had a concealable holster listed that might take care of you. Check with them. I have holsters from both and they make solid stuff.

There is a Phlster Floodlight OWB that is universal and is light specific rather than Gun specific. So if you have a TLR1 or X300 it would work.

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M&P .40, M&P 9c & Shield 45

I ended up putting a TLR1 on my 4006TSW. DeSantis makes leather light bearing holsters, but unsurprisingly not for the 4006. They do make them for the M&P and the Sig P320 though. Dimensionally they seem similar to the 4006 so I’m thinking that might work. Or is that a really bad idea?

I'd make my own with Kydex. It's a relatively easy, fun and cheap process. I've made OWB kydex holsters for my 5906 with open sight red dot and for a friend's carry HK USP with light and they work flawlessly.