Muzikat,
Sorry to hear about your inability to get 6v6 tubes from Shindo. Have you tried to get the same brand or similar tubes elsewhere? Is there anything special about the particular 6v6s that Shindo stocks?
My amp runs a very similar tube and I have been told I can use 6v6s in the amp, but, I have not tried them. The tubes I run are WE 349(four of them as output tubes). I hope your 6v6s are a lot cheaper than WE 349s.