I have no source for nylon balls, but you might try Small Parts, Inc. in Florida. Two by Four Pick a straight two by four, both from the side and front. Cut off about a 4 inch section for the recoil block. Prime the wood and paint it black or whatever color suits you. I did not use sandpaper, since I do not think appearance counts much here.
Brackets Drill a hole in one leg of each bracket about three inches from the angle.
The diameter of the hole should accommodate the bolts from the turnbuckles. The holes mark the distance the wire will be from the wood. Fasten the brackets to a centerline along the length of the two by four. Place them about 6-7 feet apart. The leg of the bracket protruding from the wood should be toward the top of the device.