There are a couple of options, but my suggestion to you is to have the barrel removed from the upper, threaded 1/2x28, and reinstalled. If a new AWB comes through, it will likely mean no more threaded barrels again...better get it threaded while you can!! You should be able to find a ton of shops that can handle it...usually costs less than $50. There should be at least a few places in vegas that could do the job. Even if it is not a gunsmith...a good machine shop should be able to do it for you.
Your only other option would be to find a "clamp-on" style brake that simply slides over the end of the barrel and is held in place by a tight allen-screw compression fit. I don't know, off hand, who is making these parts.
A forum community dedicated to Springfield Armory XD and XD-M series firearm owners and enthusiasts. Come join the discussion about optics, gunsmithing, styles, reviews, accessories, classifieds, and more!