wrote on 01.11.07 at 14:11:19:

http://cgi.ebay.co.uk/PS-2-mouse-adapter-for-Atari-ST-Free-S-H-worldwide_W0QQitemZ130166778380QQihZ003QQcategoryZ1250QQssPageNameZWDVWQQrdZ1QQcmdZViewItem Is this one?

That definitely isn't a PeST, in fact this (and quite some more stuff) comes from a guy in Poland. I haven't got one so I can't vouch for its compatibility. :/

If you want a PeST, perhaps contacting them directly at http://pest.atari.org might be better.