Hmm it's really easy. Just listen for the sound of a chest or look for a pile of them. For me to find some I go into every room not mission related usually and search every were. I have about 83. If u need help let me know

From the official guide it says that helium usually spawns near buildings that were left over before the collapse, same with the other materials, as in the ones on earth will be near mostly wreckage, the ones on venus near any overgrown plantlife and mars near cabal buildings though they don't always spawn in the same place. wasn't sure of the rest of the material names for now lol but I hope that helps at all. Temperious.

are you looking for the little yellow tubes? they kinda blend in