TS: Are you looking for a replacement mount or do you just want a riser for your existing one? Maybe these by YHM would work (the 227A model), but they only raise it 1/2 inch, not 5/8.
http://www.yankeehillmachine.com/store/rails.html
LaRue mounts are the only ones I'd pay a lot of money for. GGG makes a good one, too but I can't say if it raises the optic up any.