Also Try Mark at MCJ Imports - He had a few pairs of arches a few weeks ago - a bit pricy at £125 each though very good condition (http://www.mcjimports.co.uk)
Also try scott at VW Classics (on here) - very nice guy importing stuff from SA
Volksheaven had some at Dubfreeze but they seem to be the "left over" ones from his last shipment and not perfect (cheapish at £75 though)
As Johnny says - go for Original German rust free metal, it really is about time someone set up producing quality repair panels for EBs like you can get for splits (Autocraft, Creative eng etc)
Good luck
FS 8)