I've been looking around and found a few sites that sell it. You could try ordering from them.
google search
Just pick one of the sites and give it a try.
Your only other option is to use JB Weld and stick the broken piece back in place. I'm not sure how well it'll work tho.
By saying your outer barrel is loose, do you mean that it's wobbling side to side/up and down or just rotating around and not staying in place? If it's the former, just screw it in as far as you can, align the mag release piece with the receiver and tighten the little screw in the receiver. If it's the latter, just align the mag release with the receiver and tighten the screw.