[Jem]

You can also use that statue on the pedestal next to the vault where you find the wheel key (the one behind the curtain) in the lower level of the temple.

Or if you've got anyone with at least 50 in Alchemy, you can make one yourself. This is also a lot cheaper than buying one premade if you can even find one -- they are a bit rare.

1) Merge 2 Lt Heal + 2 Med Heal and identify the result as 2 Hvy Heal.
2) Merge one of the Hvy Heal with a Cure Lt. Condition and identify the result as a Cure Disease.
3) Merge the remaining Hvy Heal with the Cure Disease and drink the resulting Renewal Potion.