Parallel ports are ubiquitous on modern systems. Any new computer or motherboard you buy today (other than a legacy-free system) includes an IEEE 1284-compliant parallel port.
PC Parallel/Serial adapter. Very few systems require anything other than the embedded port. However, if you need to add a parallel port either to replace an older, less capable port or because you need a second parallel port to run a second printer buy one of the inexpensive (~$20) parallel/serial port cards commonly sold by computer stores and mass marketers. We've used many different ones, all of which seem to work fine and none of which is noticeably better than any of the others.
Belkin Gold Series IEEE 1284 cables. Nowadays, the only parallel cable you are likely to need is a printer cable, which is a standard off-the-shelf model. Belkin stocks a great variety of standard IEEE 1284 printer cables in lengths up to 50 feet and various combinations of Type A, B, and C connectors. Although Belkin makes a less expensive line of cables, their best grade is worth the few extra dollars it costs. Once you have one, you'll probably never need to buy a printer cable again. (http://www.belkin.com)