Thanks for the reply. There are probably quite a few companies that could make up a cable, and I may even end up making it myself out of sheer desperation... but there must be a company out there with a small stock of old interface cables. I'm told that a Commodore cable would be compatible, but again I've been unable to locate anyone who's got something similar in stock. Overall, the situation is very frustrating, and I've spent weeks searching.
Does anyone else have any suggestions?