Where can I find the most iridium?

I'm only finding Iridium in breakable, random items. Where can I find it otherwise? I assume there's some level of the mines, but which ones?

Iridium can be found and mined in the Skull Cavern in the desert. Once you have reached the bottom of the mines and fixed the bus, go to the cave in the top-left of the desert. The enemies there are tough but you're much more likely to find iridium and there's more of it the deeper you go.

Additionally, (spoiler if it is not year 3)

If you earn the best score (all four candles lit) when your grandpa evaluates you, he'll give you the Statue of Perfection which produces iridium ore.

They are very rare. I have found them in levels past 90. You can also get one from the traveling wagon sales lady. She will occasionally sell Iridium ore, bars and sprinklers.

I just got the bus fixed and it takes you to the Deseret. You can go in the cave and get Iridium drops off the mobs in there.