I have a Wilcox-Crittenden Headmate toilet installed and the seat
hinges are crap. Though the toilet is less than three years old, the
plastic hinges developed a series of cracks and one of them
broke in two. I looked around in the hardware stores but couldn't
find suitable hinges. Incidentally, my old toilet had the same
problem with broken hinges. I bought a new seat assembly for
it for 35 bucks - way too dear, IMO.

So I looked on the Internet. I found replacement hinges for less than
ten bucks on Amazon dot com.

http://www.amazon.com/dp/B000QS3JKY

They fit the existing screw holes in the seat and look like the originals.
The only difference I can see is the top lid of the seat is a little
higher in the back now. If you sit on the top lid itself for whatever reason
you might need to place an insert between the upper lid hinge arms
and the lower seat so the plastic hinge doesn't take the strain of
your weight as it would probably end up breaking.

--
Sir Gregory