It's frequency is tied to nebulae settings.

Also, increasing the frequency of other objects in relation to nebulae can decrease the frequency of nebulae and thus elerium.

1.Set mining resources to abundant

2.Get tech that increases how efficient your mining can be.

3.Make weapons choices on what is most abundant. 

I've never seen someone go omg this mining system is GREAT!!!!!.

It's kind of bad like a 4 or 5 out of 10.

My reason why I believe promethion is precious is because scientists and admins take loads of promethion to promote.   And key starbase modules burn a lot.    

You can make pretty much anything plentiful in the map settings, though.   But resources are supposed to be scarce--otherwise why have resources in the game at all?

But the things which depend on resources are disproportionate.   Power plants, prototype hyperdrives, and missiles burn gobs of antimatter.  Kinetic can burn gobs of durantium, but who cares--just don't build kinetic weapons.  Besides, you want starbases next to asteroids anyway.   I was never well into a game where I went, "ouch, I want to do this, but I just don't have enough elerium or thulium."

Elurium isnt plentiful, but you cant do much, but build weapons, thulium what its like next to promethium the most common.

So you think resources are rare huh?

Are you counting random events into your calculations?

There are events that actually spawn in more planets, anomalies, and resources.   It is infact one of the few things I consistently saw in my various playthroughs while tracking down some obnoxious bugs and whatnot.  But yea, turn up your various map settings if you want more of the resources around.  Planets too, that is why they are there.  But more importantly,  turn up the random event frequencies on that same map settings page.

Techapods and Spice have generally been my biggest issues, but on some games I get several planets with each.  It sucks to play with a tech tree requiring what you can't get, but there is a pretty good mod so you can get them from (edit)shipyard projects.