Nelson Leather made the illustrated holster for my 3" Ruger Police Service Six .357, and one for my 4" Redhawk .44 Magnum. I'm very happy with the result. Although they didn't have the one for the Service Six I sent them an e-mail and they were able to accomodate me at no extra cost. Took about three weeks.
I would have gone with Hunter, but they don't accomodate the two revolvers above, however I've been carrying my 4" Security Six in a Hunter for more years than I can remember, and recently bought one for my Single Six at Midway.
It wouldn't surprise me if Nelson could accomodate you.
Someone here on the forum put me on to them, sorry I don't recall who.
Here is the companie's link with the holster I bought for my Redhawk and Service Six:
I just ordered a Simply Rugged for a 3" S&W N frame. If Rob can build that I'm sure he can build one for the SecSix. A set of his inside/out straps and you're good to go as either a OWB pancake or IWB.
Short of that, I use a Don Hume H715-SOOT IWB for my S&W model 60 (j frame).
I asked the same ?? on another forum, and Simply Rugged won by a landslide! In fact, I found this forum because the owner -Rob- listed this as 1 of his favorites!
BTW - I ordered a pancake holster, the 'inside-out straps, some speed strips, and a pouch for them over the weekend.
At the very least, check them out and see what you think. Pricing is reasonable as well, especially considering the obvious quality of Rob's work.
Years ago I bought a Bianchi 9-2 holster.
I had to cut a little over 1/4 inch out of the cylinder recess, to make the Security Six's cylinder fit. It can also be worn as a Burns-Martin belt holster.
The Bianchi 9 is now discontinued but, can be found on E-bay, at times.