OK, so for thsoe up to date on new weapons, how about a semiautomatic Beretta Cx4 Storm Carbine? One of the optional calibres is 9x19mm, with an up to a 20 round magazine. Yiou can get it in .40 S&W and .45 ACP if you want as well. It's a ncie looking weapon, basically a carbine in pistol calibre; Shoulder stock for stability, 16 inch barrel, 31 inch total length. I'm sure that for a military contract they could shorten the barrel, and/or the stock. It comes with optional picatinny rails for modularity, too. Very easy field strip. Safety, magazine release, cocking handle, and ejector can all be switched left/right. Altogether, with a bit of Canadian adjustment, it looks like it could fulfill a PDW need. And of course, since it fires standar pistol rounds instead.
http://www.cx4storm.com/index.aspx