Don't look for "ballistic Nylon", as you may not find what you want. Rather, look for "kayak skin material" or something similar. Check with Dyson, Baidarka, and Company, as they were the major supplier of skin materials in years past. You could buy any amount of fabric that you want, perhaps even an entire bolt. If they're not selling fabric, they may be willing to tell you who their suppliers are/were. I also wouldn't limit yourself to Nylon, as polyester has properties that make is superior is some ways.