Has anyone thought about making a new serial interface card for the ][ bus? It doesn't seem like it would be a hard thing to stick a uart, a canned 1.8432MHz oscillator, one of those max232 line buffer/driver chips, and a small eprom on a small card these days. A uart like a 6551 or 6851 (or ugh! even a 16550) ought to make the firmware easy. I know of at least one place (expressPCB) that provides free software that lets you lay out a card and then they etch them for you, cheap, and supposedly double sided and through-hole plated, too. Can you etch edge connectors on those things?
I know, I know, you can probably still get an SSC on ebay, but where's the challenge in that?