Mike I sell solid copper rockerbox gaskets, they are Lazer cut C106 soft copper so they do not need to be annealed, they are £16-00 a set plus p+p, I can take pay pal as a gift, to JOGI102@aol.com these are well tested and work very well, I have not had one leak yet.
C106 copper has a hardness range of 40 - 160 Vickers. Most C106 copper as supplied is not near the soft end of that range. The vacuum hardened ones that Ebor Bikes sell typically test at about 42 Vickers and are remarkably soft. They cost £17.60 a set plus P&P.