As MHC says, there might be a card you can recover from an old PC if you are after a PCI card. If you need a PCI Express card, you'll probably need to buy one. I've had success with serial cards from
Lindy - they have a range of
parallel port cards and
serial/parallel combo cards, which you might find available cheaper from resellers than their online store.
Before buying any card, it's a good idea to establish the driver status for the desired operating system by checking the available downloads on the manufacturers' site. There's several manufacturers of the chipsets used on these cards, including Oxford (now part of PLX Technology) and MOSchip.
I know rather more about the Oxford based cards, as I wrote the patch that added driver support for the Oxford PCI Express multi-port serial cards to FreeBSD. PLX make generic drivers and data sheets freely available to anyone that registers, which often gives you a route to use cards on operating systems after the manufacturer drops driver support.