Volterra card

The official tourism website doesn't have a section specific to the card but it is mentioned in the ticketing info for each of the attractions it covers, such as the Guarnacci Museum:

https://volterratur.it/en/poi/guarnacci-etruscan-museum/

There also doesn't appear to be any need to purchase any attraction tickets or the card in advance. This traveler states that it "can be purchased at any site that accepts the card", and did so at one of them themselves.

https://www.earthtrekkers.com/best-things-to-do-in-volterra-italy/

I'm sure you could also purchase one at the tourism office in Volterra but you could email them for confirmation if desired?
https://volterratur.it/en/our-tourist-offices/

Awesome, thanks Kathy!