All the connectors (both for the data and the 4 pin power as well) are relatively standard - you can buy them in single quantity from Mouser in the USA. The IDE connector is just a 2x20 0.1" IDC ribbon connector. You'd have to get the necessary length of ribbon cable, as well, and I don't know of any places online that sell that by the foot (I'm sure someone else does). You can crimp the IDCs on with a bench vise or even a pair of pliers if you're careful, no need for a "real" crimper here. Making a cable of the correct length is almost certainly a better idea than trying to extend "normal" length ones.
However, be aware that IDE isn't designed to go that far. That's why they don't make IDE cables this long. It'll probably work just fine, but it may not, especially if the inside of your cab is electrically noisy (which it often is). If it's flakey, keep bumping the speed/mode down (PIO mode 2 or slower is almost guaranteed to work even on crappy cabling, while UDMA is probably going to be questionable). Also, if you can find the connectors for it (I think Mouser has these, too) use some of the 80 conductor half-pitch cable. That helps a lot with signal integrity.