dave weil said:

Basically, what I'm saying is that you can search for 12AX7s on eBay,
I guess.

I'd strongly recommend that one buys tubes NOT from Ebay.
Practices like selling old, worn out tubes with new logos and freshly
golded pins are not that unusual.
Go with a reputable vendor like Ned Carlson www.triodeelectronics.com
or perhaps Willie "Lord Valve" if you can stand his attitude :-)
These guys don't just sell, but can also advise you better than anyone
in this newsgroup, including myself.

BTW Powell, 12 AX7s in a microphone amp, are you seriously looking for
noise and microphony? :-)
In any case, when the design calls for AX7, try 7025 RCA.

For a microphone amp, a better choice would be EF86 in triode, IMHO.

--
Sander deWaal
Vacuum Audio Consultancy