Can't find Ritual Stones with needed high tier rolls

I’m trying to upgrade my Fragment of the Enigma with a good ritual stone base, but I can’t for the life of me get one to drop.

Is this bugged, or am I just having the worst luck trying to farm one?

I’ve verified my loot filter is working correctly by dropping something similar I bought from a vendor, and when I had the tier lowered it showed up.

Hi, first of all - you don’t need exact base, any catalyst will do.

hmm, I could have sworn the required base had to be the same as the Unique. Thanks.

Nope, just the same item type (relic, 1h sword, 2h mace, body armour, etc).