After a fresh server wipe you can find plenty yellow protective cases but after a few weeks, some objects like these seem much harder to find (if you can find them at all...) It seems like there's a hard limit on servers and when hoarders in bases got them all, they won't spawn anymore.
I don't build bases (I’d rather destroy them) but I do like to make some improvised explosives :) Unfortunately, when I can't find one single required crafting item because of HOARDERS, I can't make them anymore.
Perhaps it would be a good idea to reconsider whether the hard limit for protective cases is still needed, because nowadays you can also use them for other things then just storing items.