The two-tailed rockshot whatchamacallits in the crystal desert drop bleached CARAPACES, not bleached SHELLS. I made that mistake and spent a bunch of time collecting 5 bleached carapaces, thinking the collector would trade them for a nice helm. He doesn't take carapaces, and I don't know where bleached shells are.
I got 1 Bleached Shell, from a chest sadly... so I don't know who drops them. I tried salvaging Bleached Carapaces (I thought Bleached Carapaces = Bleached Shells too) and only got Shells.
According to a post on gwonline, Sand Wurms drop the bleached shells. I saw one only once, and didn't want to mess with it. Apparently they have lots of knockdowns, so be prepared.
It is a bit annoying that warrior's wanting the +1 sword helm (don't know what it is for other classes) have to go after something so hard to find - at least I haven't found anywhere they show up a lot at. I know where to get the stuff for the other helms...they're all relatively easy since you can find the relevant mobs easily enough.
Im finding it very hard for siege wrums to drop it now. I just killed 20 siege wrums (solo) and keep getting items rather than the bleached shell... is there something wrong here?