I bought from some company online a lot of 3/32" stainless cable, 100 thimbles (the little tear-drop shaped things), and 100 brass ferrules. For my rim and the size of my hub, a 48.5" piece of cable is enough to attach to the rim in the middle of the cable, and then on the other ends I attach turnbuckles. These equate to my wheel's nipples.
I have also attached a picture of the tool I made to crimp the ferrules. It's just a cheap pair of bolt cutters that I disassembled, ground notches into the teeth, and then reassembled.