The new Colt Mustang Pocketlight is exactly the same as the old Colt Mustang and Mustang Pocketlight. It so happens that I have been looking for an OWB belt holster for the sister pistol, the Colt Pony, and I have found that very few of the "name" (or no-name) holster makers offer a holster for the Mustang or the Pony.
The frame of the Mustang is the same as the Government .380, but the slide and barrel of the Mustang are shorter. A holster for a Government .380 will work, if you can find one, but if it's a closed muzzle design there will be empty space beyond the Mustang's muzzle, and eventually the end of the holster will get mashed.
I'm about to order one of these, from Bulldog Cases. It's cheap enough that, if it doesn't work, I won't cry a river of salty tears.
The web site is
http://www.bulldogcases.com/case-vau...ort=20a&page=2 . For the Mustang, the size would be the small. It's available directly from Bulldog, it's cheaper at Sportsmans Guide, and even cheaper yet at Optics Planet:
http://www.opticsplanet.com/reviews/...ini-autos.html