I think they are Drifta...I have only seen them once at a large pet/fish store near Hartford, Ct....but you may be able to get them if you ask the store to order some for you. Some stores will do that.
My multies are usually out of their shells unless they sense danger which relates to movement close to their tank. Once you become still, they come back out, at least with the multies. A place recommended a lot on the shellie site to order them online if you can't get them locally is Wet Thumb Aquatics