What about the
cartridges?
They can be found. There were some on E-bay recently. They turn up at
hamfest and surplus outlets.
Isn't it just a standard DC-100 cartridge? AFAIK, those are still being
made. Of course, it's undoubtedly cheaper to get them at a hamfest.
Unfortunately some HP systems (and some other vendors' systems as well)
require preformatted tapes. I hope the HP-85 doesn't need that.
I'm told that the HP 9133 (or was it 9144?) does.