I'm looking for a new Case toliet seat also. Mine
has an elongated bowl of specific dimensions AND
the hinges go into the tank instead of downward
as normal. I did find on a website that offered
Case toliet parts but they didn't have my toliet
bowl size. It was either "plumbingsupply.com" or
"plumbingwarehouse.com" - it leads to the same
site. The downside is that the seats are $99.00
each (if they have your size) but then that beats
putting in a whole new toliet!
Our half-bath has a Case toliet and we were able
to use a regular, elongated toliet seat on it (it
has downward hinges).