Arsenic - incredibly hard to farm

[Valorin]

Arsenic is actually not hard to find. I got most of mine at lava spouts actually, in the crystals there. There are a few spots which also have a tourist beacon, which also makes them easy to find. Try Upsilon Phoenicis. First planet I think. Tourist beacon is targetable from the Navigation panel.

 

[Red Anders]

I believe it's polonium you're after.
1 polonium = 9 arsenic, unless they changed it.
Since we find them in "3s" 1 polonium hit is actually 27 arsenic.

Wahay! I knew keeping 50-odd units of polonium in my mat store this last year would pay off eventually.

 

[zarrazee]

...Abnormal compact emission data. g impossible to find man.

I got 17.