Here's my option for a free float forearm:
http://troyind.com/%20/rail-systemsa...%B3-with-sight
Granted, it's 1" shorter than you'd like, but 13" is not bad. It is pricey at $283, but the flip up front sight will save you money if you don't already own a front sight you like. I have a Troy 9" rail and really like it, and if I ever upgraded this is the one I'd get. It's also modular, so you can throw rail sections on it where every you'd like.