ive asked before for this, and i never found it in any place i looked
i asked around for some since a friend of mine needed one to unban a 360 console / or try to at least
I looked around for one some 8 months ago so i doubt that suddenyl the shops will have have them
this isn't standard hardware for users to use anyway.
i hear you can do this with a NORway on Teensy++ 2.0; but im not so sure.
refer to this, and i hope you end up finding one:
http://gbatemp.net/t305355-ps3-v3-70-downgrade-method-released?&st=0