I've been farming flame geodes on firesday whenever it happens to line up with my schedule and I'm not doing anything else. I'll usually get 1 maybe 2 geodes with the rare 3rd geode if the random number generator smiles upon me. Last night I was farming during firesday and a heat spell actually showed up. I got 5 geodes before the day ended. So yeah, if fire weather were actually common, people could reliably farm up their own just like any other geode if they so choose, instead of relying on them showing up on the AH from some guy that had it drop to them in an AFK exp party or something.