a few hermits - scarlet reefs, blue, green, and red legged hermits
snails - turbo, nassarius, and cerith snails
How many of each depends on how large your tank is. They dont add much in the way of bioload but if there are too many they may starve and die off, or the crabs may start eating your snails.
I know one of the vendors on here has a website and specializes in CUCs, but I cant remember for the life of me who it is.