12AT7 tubes can be called different things, but I am not aware of any substitutes. For example, 6201 is US mil-spec AT and ECC81 is euro designation. .
I have a bunch of US ATs and a fair number of Amperex/Philips/Valvo.
You might want to post a wanted ad with the specifics of what you are looking for. The admins don't want us dealing direct. I would be happy to post a listing if you let me know what you want.