I have had the Cronus Mag II for almost 4 years now. Excellent!
Cryo Tungsol KT120, Upscale audio, Kevin has them, last I checked. I have extra sets now.
Prices are getting very stupid high I have seen a quad for $400+ as high as $1K. Stay away from these rip off dealers. I think that was Viva tubes.
What I use is a little different but very satisfying. I know Mark O'Brien from Rogue likes Telefunken in this Amp
left and right front RCA 5963 (1957 computer tubes) center Telefunken NOS Ribbed plate 12AU7/ ECC82
Front Telefunken NOS ribbed plate 12AX7. I think they are labeled "Fisher" 60's?
Brent Jessy has these tubes all tested. Not cheap.
Same combo as above but just substituting the (top middle) with these.
Also Tungsram NOS ECC82/12AU7 must have a number tab inside the strut to top getter.
There are Funkworks relabeled Tungsram out there. No number tab. You need to watch everything even at dealers I have found this.
RCA Clear top 12Au7 a bit bright sounding but nice depending on front end and speakers
NOS Mullard CV4003 to dull soft sounding here and expensive.
Genalex Gold Lion B749/ECC82/12AU7 gold pin reissues, very nice, But Russian may be hard to get now $50 each
All this to your taste, speakers, front end equipment choices etc. etc.