I know Amazon eventually obsoletes older versions, but I thought maybe you knew of a recent enough build which still works on your OS.
Didn't think to check/ask for confirmation.

A faintly ridiculous thought, maybe, but what are the odds that you could get the
Windows version of Kindle for PC working through
WINE?
WINE on linux is how I run K4PC (experimental purposes, as I have the E-Ink KT as well).
It works fine -- should work on OSX as well, as long as WINE still supports OSX 10.6 Snow Leopard.