Well, it’s a 12AX7 in the pre-amp, so these are certainly obtainable.

The high-end EHX version would be the gold-pin:

https://www.ehx.com/products/12ax7-gold

From personal experience with their tube pedals, I can say that EHX tubes are reliable and sound great. It also costs about $17.00.

Hard-core purists would probably suggest an eBay search for NOS versions of the tube it originally came with, if you’re in the mood for a difficult and expensive adventure (not being sarcastic, some people really like this kind of thing).

THe other nice thing is that a 12AY7 is probably (check this) compatible if you want to experiment with a smoother, lower gain sound, which also are cheap and easy to find.