You just need the cable's gauge (10 ?) and the dimension of the battery's post (1/4"?) and you can get one at Home Depot, Platt Electric, Napa, Cut Rate, on and on, etc. ad nauseum. Soldering after crimping it on is good too. An electrical supply such as Platt is probably the best bet for the insulator. I'm a hillbilly, I would use shrink tube slid up the wire until I got the lug on, slide it down, heat gun it and ride.
