hmmm... you said "aging". Time to get rid of them old tubes.
I'm not sure if tubes can still be found in raon, I understand that the issue with some el cheapo tubes is finding a matched pair.
You should try audiophile, last i looked they had tubes, and check with the high-end audio shops at park square that sell hi-fi tube amps.
Or, pm deltaslim, he used to sell lotsa tubes.