Good question?
I just order a cheap one off of ebay for my 308.
I thought I would give it a try. Can't go too wrong for what I paid.
Jerry Miculek 30cal brake for $59. plus $6 shipping.
I got mine from there as well, came with crush washer and all. Works well!
That sounds like a pretty good brake now that I have read up on them. Looking at the dpms version any canadian vendors carry these