I think you could modify and AR-15 to .32 ACP pretty easily. As Bwana John notes .32 ACP bullets are .312" diameter, and can be pushed through a standard .308" diameter 30 caliber barrel. I'd wager they'd work better in an Eastern European / Russian 30 caliber barrel which actually is .312" dimater.
My thoughts are to start with an existing 9mm AR-15 bolt and modify the extractor and bolt face for .32 ACP. I don't think that would require too much work because the .32 ACP is semi-rimmed, so the base diameter isn't that far off from 9x19.
Next, get a 7.62x39 AR-15 barrel blank, have the breech face machined to match your bolt, and then cut a .32 ACP chamber of course.
I see two ways to go about the magazine. One is take an existing .32 ACP magazine like that of the Czech Skorpion and weld on a sheet metal block at the top to fit the AR-15 mag well, or have a mag well block machined from a metal or polymer billet so you could use unmodified magazines. The other is to take the Black Dog Machine / CMMG pattern magazine and slightly scale it up for .32 ACP. I think a good machinist could mill such a mag out of Delrin pretty easily. You could probably even use off the shelf BDM / CMMG .22 LR mag springs with an appropriate follower and slightly reduced capacity for the additional weight of the .32 ACP rounds.
It wouldn't be a cheap project, but it would probably be far less expensive than tracking down one of the rare carbines already mentioned.