I don't think there's a specific place or something. Just fly to every cave you see on the map, dig all the veins you can and restart the mission if you need more minerals and you run out of caves. It's a slow and tedious process, but I doubt you can make it any faster.

When you exit the gate, look to the left (South). There is a cave near the Transport Depot that has a decent amount of ore and gems. It also has a fishing spot that spawns charamotes.

They show up wherever for the most part. Though big tip when it comes to Hesperon which is pretty rare. The lake/pond near the temple of profit red veins there often have it. It's needed for a couple frames and it's one of the only things on orb vallis I had to go out looking for.

There are also some crates that drop resources scattered around orb vallis and I think the orbs drop some stuff too if you don't want to mine/fish.