Couldn’t find anywhere to order a longer cable with a shielded single pair of wires heavy enough to power the motor. Sent an email to Super Droid Robots asking if I could get a longer cable from them.
Also having trouble finding cable for the encoders. The original cables have four pairs of twisted wires and the whole thing is wrapped in foil. Found a place online to order cables, but the price was fairly high for the number of feet I need. Finally found the best solution – it turns out that ethernet cable also has four pairs of twisted wires. If you get CAT6 ethernet cable, it is shielded. Now I just have to find some cheap, shielded ethernet cable.