Angry gun will be releasing an L119A2 front rail in the next few weeks through Redwolf UK. As of yet the price isn't confirmed but rumored to be around the £120 mark. These will attach to a barrel nut creating the illusion of a 1 piece upper. Both the CQB (10 inch) length and the carbine length (16 inch) will be made.
Here are a few photo's of the pre-production version attached to a TM NGRS M4.