Just found this...
https://code.google.com/archive/p/pr...wnloads?page=5
I don't think it was there before.
I might go here and download the firmware for the various Sony Readers before this link disappears.
EDIT: Looks like there are only firmware updaters for the PRS-350, PRS-650 and PRS-950, but at least that's something. I'm guessing these are U.S. firmware releases?