Pink Floyd who runs the Rock Grotto site and developed mods for the X-Can amps recommends Russian 6N23P tunes from the Voskhod plant. He sells them for 22 pounds for a pair. I just bought some on ebay for $20 US shipped from Ukraine. They seemed to have the correct logos and the seller had 100% feedback. But I guess I won't know what they're like till the get here in a couple of weeks.
Edit: the guy just sent me an email saying that my tubes had shipped complete with a photo of my package!