I had a machinist friend of mine make up a batch of a half dozen mk1 muzzle brakes a few months ago. I have two left available, but they are not cheap: $550 plus postage (postage to the UK on these starts at around $35 or so for 8 day or less small packet). They are a very very exact copy. One of the purchasers out of the UK mentioned he had been looking for one of these for about 8 years.
Here is a shot of one still in the white next to my original. They have since been blued.
In the thumbnail below is a shot of the brake on a UK customer's rifle.