Get some male solderless molex pin connectors and a female four pin Molex connector. Wire up the joysticks to the pins inside the Molex and plug a standard PC connector into it (the 5v is usually the red wire, the two black are ground and then the yellow is 12v-check it with a multimeter to be positive, however).
Assuming the guys who work at your local Radio Shack are proper geeks, they should be able to point you to what you need, but it's at a premium price. If you have a Fry's nearby, they stock the stuff for less, but you are a lot less likely to find someone who can help you buy the stuff if you don't know what you are looking for. Absolute worst case, I could probably sell you what you would need for a few bucks + postage.