I would highly doubt that there are many, if any at all, direct blowback .223 carbines. Like others have said, I think the H&K roller-lock design would be about as close as you're going to get to one.
When I was reading a book about the H&K MP5, they went into the history of the G3/HK91 rifle. It mentioned that if it were a straight blowback weapon, the bolt would need to be 43 lbs in order to keep the chamber closed until the pressure dropped to safe levels. I know .223 isn't a .308, but I would imagine the bolt weight would still have to be significant, probably weight prohibitive, to accomplish the same thing.