I just ordered a Bushmaster upper from EF last Friday. Should be getting it this Friday. Ask them if they have what you need. I sent off a quick email asking if they had a particular upper that Bushmaster makes but doesn't advertise in their catalogs. Not only did they have it, they had two. Beat BM's price on it too.
Not to knock BM direct, I did buy a M4/Patrolman's Carbine upper from them for my Sunset Celebration rifle. BM does such a good job that sometimes it's worth it to pay a few extra dollars to say "thanks."
But definitely check EF out. They did me right, and I'll probably get another upper (an A2 Dissy) from them in December.