Some time ago I made the flail snail on the right; more recently I made a second, more naturalistic flail snail.
Click to embiggen … at your peril!
The new one, on the left, has a real seashell for its shell (lightly washed with dark brown), and the body is made of polymer clay. The flails were also polymer clay, formed around some florist wire so they’d be less likely to break, and to give them an easy way to attach. The older one, on the right, has a shell from a cheap plastic animal, a body of epoxy putty, and the flails are wire with mace-heads from cheap plastic knight toys.
While I have no doubt that others have made their own flail snail minis (this lovely one came up early in a GIS), I do find it odd that no miniatures company ever made them. They hardly require much skill, though I guess as one of the infamously “dumbest monsters of D&D” lists, and an example of what’s so terrible about the Fiend Folio, the poor flail snail is subject to too much ridicule to get a fair break.
Swords & Dorkery 
I am ashamed to admit that when the Fiend Folio first came out, I thought many of the monsters (including the flail snail) were ‘dumb’ and ‘unrealistic.’ Eventually I realized that I was being a young, over opinionated tight-ass and now I love the flail snail, in all of it’s flailing, snailing glory.
Forgot to add before I hit ‘post’ that I like your flail snails (both models) and would like to +1 them.
Thanks!
Really cool idea to make those yourself with some real shells. Are the flail heads supposed to be me metal or organic? The concept is silly, but that is what I love about DnD. Sealions anyone :D.
Thanks! I think of the flail heads as inorganic, possibly something mineral the snail secretes like the shell. But I don’t think too deeply about them.
Possibly one should not think to deeply about flail snails ;). It is the path to insanity .