From Rebirth of the Night Wiki

Hi, I'm not finding any iron after a decent-ish time of looking and was wondering if there were some changes to ore generation that would explain it. Thanks for any help.

Response to finding iron[edit]

I don't know if this will work as an answer since I don't see a reply button. In any case, iron in RotN generates at a lower altitude than in vanilla MC, but it is just as or more common. On top of that certain biomes have different spawning conditions for ores, as you can see here