Why not build one Joey. You can order an upper receiver assembly built the way you want it directly from Bushmaster. Then just buy a complete lower receiver from a local dealer, (they may have to order it, check with J&G for a price), and put it together. It will cost you about the same as a new rifle and you get it the way you want right off the bat.
After the ban expires you can put what ever you want on it. You're still required to follow the regular rules, barrel length not less than 16 inches, ect.. etc.