Right now Eyegore has a Group Buy going for some unpainted, foam skulls under the Group Buy area (min. qty of 10). If you don't want to bother with painting your skulls and are looking for plastic ones instead, the online DOLLAR TREE website has a case of 16 of them available for UPS delivery only (sometimes you can save on shipping by having it delivered to the store for pickup but not in this case). I would not expect to see these in the store given the shipping restriction on them.

BTW these aren't the alien-looking skulls that they have carried in the past. I think the foam skulls in the GB look more realistic, but these DT ones aren't that bad. Here's the link, and I would think these will sell out quickly online just like Eyegore's GB has exploded in just a day.

Dollar Tree 7-1/2 inch Plastic Halloween Skulls Bulk Item