Here is a link to an old post at Audiogon back in 2001, where much of my tube preferences for the Aesthetix are discussed.
http://audiogo1.iserver.net/cgi-bin/forum5.pl?aamps&980918116&read&keyw&zzaesthetixThe EL 34 is vital to the test and must be replaced before you can test the other types. The GE 5692 is the worst choice in that position, the RCA and Sylvania as well as the VT 231 types are all superior.
Aftermarket vendors for NOS tubes include Vintage Tube (Andy Bauwman) at 616-454-3467 and BWS (Bruce Wenger) at 703-536-3910.
Both are good friends of mine, both extremely knowledgeable about all types of tubes. Try them and see if they have what you need. Obviously since none of these tubes have been made in many years the supplies are variable and may not be available when you want them.