I had a similar problem with the cable for the HP 48. However, in this case it turned out that the serial pinout was known and a connector could be made out of a PC motherboard connector (for speakers, etc.) plus a cut-up RS232 cable. It was nice to be able to download stuff into my calculator using a PC serial transfer program (I forget the protocol.)
I also made a cable for my HP 48SX. I also used individual female pins from some other connector, soldered the wires to them and then I molded an epoxy "body" on top of them while they were plugged into the calculator (talk about living on the edge).
I still have the calculator and the cable. For some time the calculator had some display issues after being accidentally dropped but I powered it up a few months back and it seems to have fixed itself. I recall how much I wanted to get one back in the day and how much fun it was.
