Well, it sounds like the Clipdraw attachment which is sold for several popular handguns. Basically a metal clip similar to the ones on many folding knives and originally pioneered by Spyderco, I believe. They attach next to, or under, the regular grips on the gun, and are usually used like an IWB holster...sort of a safer form of "mexican" carry.
My only concern with it would be just how strong the clip was in regard to the weight of the weapon. Not to mention just how strong your pocket or waistband is...it would be rather embarrassing to not only have the gun hit the pavement, but to have your trousers fall apart at the same time!
On another note, I have...just once or twice...carried an SWD M-12 and found that it fits rather nicely in a cordless drill holster from the hardware store.
(For those unfamiliar with it, the M-12 is the semi-automatic .380 caliber "little brother" of the MAC-10. They were made by several companies and usually sold under the "Cobray" brand name.