I bought it on ebay - there are many russian, ukraine and other sellers selling russian 6N1P and 6N6P tubes. I never got any bad experience with these guys.
Novosibirsk 6N1P, matched pair from 1960s:
Voshkod pair 6N1P-EV from 1975:
I also bought the same year Novosibirsk 6N6P power tubes, because the stock tubes i got had about 5 years of difference in year production:
These power tubes are liitle bit better than stock, but its very subtle difference. I also tried Foton 6N6P power tubes, it got little bit tighter sound but less subbas extension, but difference in power tubes is very very subtle - still hearable.
Difference between 6N1P and 6CG7 is big in sound character - but you have to decide what is good for you, also it very depends what suits your headphones. Maybe try to get 6N1P + 6N6P first from one seller, if you are going to get 6N6P anyway and you will see. Tung-sols 6CG7 are much more expensive. Some people dont like their big soundstage (maybe distant soundstage in front of you). 6N1P does have totally different soundstage - very close and around you. It is the biggest difference between both.