Apart from my local stationers / art shop, I only know of Silverprint, the latter stocking a very limited range of Arches Platine and Cranes Parchment. Maybe those that participate in the Alternate Print Exchange, such as Carl, Phill, or John will come in with specific help.
As an aside have you looked at Ed Buffalo’s site, for he has several pages devoted to this process?
http://unblinkingeye.com/Articles/Cyano/cyano.html