The link to the Reference Card at bitsavers appears to be an IBM
reference card (very nice, thanks!) but not the one you are seeking. I
remember the small white card and I think I still have one. I will try
to find it and scan/photo it for you if I find it. It was indeed the
size of a credit card, but thinner of course. I don't recall where I got
mine - perhaps Ken gave them out at IPSA - I think I would have
remembered him doing that! Oh well, I seem to have memory parity errors too.