I found this thread on google but figured I would drop in because I found an anti-glare screen for the prs-600 the other day and ordered it. Got it today, pretty good, I am happy with it:
http://www.amazon.com/Lexerd-PRS-600...3957109&sr=8-2
There is the link, as far as I can tell they seem to be the only person selling it.
I hope that helps.