Might check the provided link below. I found it to be helpful and reasonably accurate in tube gain. Like millercarbon said, it can get expensive. I was looking for more high frequency detail. I found new production Mullards to lack the dynamics I wanted. I have Bob Carver mono blocks that use KT88s. Purchased used. Previous owner had already upgraded the tubes. The KT88s were Gold Lion. The 12AX7s were some old stock Millard medical grade tubes. After rolling tubes, I ended up liking the sound of new production Gold Lions. Actually have replaced the tubes in Manley Chinook with the Gold Lions as well. The Gold Lions have more gain at higher frequencies. Hope you find what suites. Happy Listening!
https://www.scribd.com/document/383393010/12ax7-Comparison-of-Current-Made-Tubes-2016-1
https://www.scribd.com/document/383393010/12ax7-Comparison-of-Current-Made-Tubes-2016-1