There are plenty of mini-DIN connectors and serial cables for mac on ebay.

You need just three wires for serial line to work. I would strip the wires and plug them in without any connector. :)

Classic macs had RS-422 not RS-232 ports so you'll need more than just a dumb cable to get it working with a PC.

You are right, but it's possible to connect RS-422 to RS-232 using just proper wiring [1]. Basically, same three wires and one loop wire for RX+ to ground. It's not reliable and not recommended, but works and would solve the problem. :-)

1. https://stratusengineering.com/rs232-rs422485-conversion-cab...

The Mac RS-422 ports are backwards compatible with RS-232, dumb cables work fine. No Mac users were buying special RS-422 modems back in the day, we all used standard PC RS-232 modems and they worked fine with just a dumb cable. Even Apple's own serial printers were just RS-232.

A Farallon EtherWave provides Ethernet directly.