Nope, the only KT mags that are avilabile are the stock ones (6 rounders). I think that there are mags from Bersa or another 380 manufacturer that will fit in the P3AT but I can't remember who they are. I am sure that Flyer will chime in here and he knows who they are.
The +1 extensions work out pretty nicely, actually. I had some initial problems with the "L" shaped spring base, but after bending it in a little and filing the lip to make it as flush with the mag body as possible, it works quite nicely.
IF you're going to use the +1, it would be a VERY good idea to take an exacto knife and **carefully** remove a bit of material from the hammer spring catch (part 79, sits at the bottom rear of the grip). Removing a small amount of material adjacent to the magazine well allows mag to seat without the lip of the +1 snagging on the hammer spring catch. This avoids bending the +1 leg outwards, which would necessitate disassembling the mag to re-bend it.
It also ensures that if you're using a +1 as your backup mag that it will seat positively in an emergency.
I did this procedure because I initially had problems with the mag not seating well and thus not positively engaging the catch, which didn't bode well for a reload under stress.