Serial port for laptop

I have a laptop with one serial port. But I need a second serial port. Which is the alternative to get a second one? My laptop have 4 USB ports, one parallel port ans 1 serial port. Could I find a QNX6 driver for PCMCIA card or USB-Serial converter?

I have used PCMCIA serial card in the past, no problem to report. I think they were sold by black box