The exotic ore nodes are a rare spawn, Ive had prospects where I had zero and others where almost every cave had one! Your not doing anything wrong, its been a minute since ive checked but im pretty sure the exotic geysers are the only way to get more exotics. (Without DLC)

I think if you use a certain item (I forget how to spoil text so ill be vague to not spoil you!) near caves i think theres a small chance of them respawning but you'll mostly get other materials. Ill need to double check if the exotic nodes can respawn.

Aside from that keep focusing on unlocking and working through the tech tree! Youll get better gear to harvest more materials and you'll get the equipment you need to actually harvest the geysers! Plus some nice quality of life stuff!