Pulcher doesn't need shells, just a cave to breed in. I haven't kept the other two, but n. kungweensis is listed as laying eggs in shells by Konings. Probably the standard shells (escargot, etc) would work for them.
Pulcher will be happy with a pile of rocks, kungweensis may use rocks or shells, and callipterus need a pretty big tank, I would say 75g. for 1 male and a harem of females, and a huge tank for multiple males, the females would use escargots.