Is there such a thing and if so where can you get one?
Yes and no or maybe.
Colt exports 9mms w/flat tops but no domestic sales (=yes they exist but no you can’t have one).
There is allegedly one on the prodution line as we speak for domestic sales as I type; no word on parts (i.e. uppers) making it to the market anytime soon (=maybe (someday)).
Can’t you build one of these on a Colt flat top stripped upper? Get all the Colt parts from SAW?
The standard M4 upper intended for rifle calibers (i.e. 5.56) differs in several ways from the upper intended for 9mm. Among the differences are no brass deflector or forward assist, and no gas tube hole. I think I have pictures somewhere of some of the differences. Some people still have successfully used them, but personally I’d just buy a stripped flattop 9mm upper from RRA and change it out on the Colt.
Thanks for the replies. I will be buying the rock river 9mm upper.