Are you sure you were looking at a Corona, not a Carolina or Captiva?

The older Corona is basically indistinguishable from the Eclipse 14.5, with
the exception of a slightly better seat.

Do retailes stock any additional thin seat padding?

There are a lot of nice seating options, although fit it more important than
thickness of padding. That said, I'm a pretty big fan of the Sealine (???)
seat pads, it works like a thermarest sleeping pad. Let in inflate, open
the valve, sit, close valve, quick, near perfect fit.

Geoff