Tom and anyone else who might be interested...
I purchased 500 feet of 3/16", Black, Dacron Polyester rope from the
following source on eBay, and I am very satisfied with it:
Seller: k4ibw
Description: Antenna Support Rope Black Dacron Polyester 3 16"X500' | eBay
http://www.ebay.com/itm/Antenna-support-rope-black-dacron-polyester-3-16-x50
0-/281610280058?pt=US_Radio_Comm_Antennas&hash=item419147dc7a#mainContent