There are just not many 45acp semi auto carbines manufactured. The magazine size is large and doesn't fit many of the popular current receivers like the AR15 or MP5.
Other than the KRISS you mentioned the MAC10 style guns are still made along with some specialty AR's in 45acp like Olympic Arms. The long discontinued Marlin Camp Carbine comes to mind but the recoil spring & buffer require attention.
The problem I see with blowback guns and a can is very rapid fouling, man they get dirty fast. Hell even the MP5 when suppressed is a nasty mess after a mag or 2 and its a roller locked action. The other thing to consider is bolt weight or mass, the MAC10 bolt is pretty heavy which creates a lot of inertia as the gun is fired and moves the gun around.
The 9mm guns don't suffer (as much) from this bolt mass issue and in the AR platform hydraulic buffers will smooth things out. I enjoy the 45 cal guns but shoot more suppressed 9 mm and I think a 9 sounds better than a 45 when suppressed or at least it's easier to suppress well vs a 45acp. There seems to be an endless variety of quality cans available for the 9mm as opposed to only a couple of top tier cans that work well in 45acp. So you'll spend more money to suppress that 45 over a 9.
Personally I'd look at the new Sig MPX in 9mm once released it should be the ticket with a can!
