USB to serial adapters. They work with Linux. I've used about 10 different models. Seems to only be about 2 or 3 chipsets. All worked good, last year (March or so) was the last time I used one though.
If you want, contact me off forums (e-mail down below) and we can arrange for shipping and handling.
Or you can goto $ELECTRONICS_RETAILER and buy one for similar costs.
Or you can go online and buy one of many from sources. Similar costs, again.
And, yes USB has taken over that realm. The only *real* serial ports these days, are ones on motherboards that can re-direct console output to the serial port. They work regularly, too.
Also, a couple of other cheery things I'd like to chat with you about.