Most copper based greases are pants, and arn't really suitable for use as an anti-seize lubricant on brakes. You really need a lead-free nickel based grease.
I personally use, and highly recommend "Bostick Never-Seez - Pure Nickel Special". It ain't cheap, but it really is miles better than any copper grease. I get mine from Cromwell Industrial Supplies - look at
www.Cromwell.co.uk to find your local branch. You can also download the lubricants section of their catalogue here:
http://www.cromwell.co.uk/images/publication/pdf/cat2009/07.pdf, and find it on page 1270.
HTH
