The Hunt begins for rare materials

So I have found the FSD boost (basic) extremely useful for turning my Corvette into a useful trader. Unfortunately I want to turn it into a good trader and would like to stock up on

Arsenic
Niobium
Yttrium
Polonium

Now Arsenic I have some of but the other three I can't find anywhere on the surface worlds.

So I've spend some some browsing the Universal Cartographics database.

I'm going to try a metal rich world like the one below orbiting Dulos.

I need to find somewhere less Imperial though!