a while ago there was a thread where someone was searching for an HP-48GX
Currently there are at least two 128K cards and one 1MB card on the
well-known auction site.
No, I'm _not_ the seller, and I don't get profit for pointing to the cards.
But I know the seller is reliable, as I bought some HP-48GX units
with Black/White high contrast display from him in the past.