these are going to be tough to source, they didnt sell a lot of them to begin with, and aftermarket on these has been thin even when new. 14 years later, who knows. You might widen your search terms to 'Norge' instead of 'Breva' for a little better luck.
I know some folks have used sockets as risers with longer bolts. IIRC the top of the upper clamp is flat, you may be able to have some fabricated from thick aluminum plate, or do so yourself with a drill press and angle grinder.