If nothing else comes up I guess we can use pistol carbine chassis things, don't know what the general term for them would be. A modern take on the old shoulder stocked Hi-powers and Broom Handles. This unit is a CAA MCK, P320 version though they do them for a bunch of handguns.
There is also the B+T P320 Grip Module with side-folding Buttstock. Unlike some conversions, this one has a reasonable Lenght of Pull which does not require the firer to "scrunch up" on the rear of the gun. It is a more minimalist approach to the PDW/PCC than some of the others, being just a grip module.


Of course, there is always the King of the Pistol-based PDW/PCCs if you have the spare scratch - the SIG Legion Flux Raider priced at a cool $2600 CAD without the $500 USD Fire Control Unit (the serialized P320 "firearm"):
