Any place that sells ATV/snowmobile parts should have one.I prefer the red NGK racing cables and you just cut them to the length you need.They come in a 90 degree or straight boot.Go with the 90 degree.They,re a tad bigger but if you spray some wd 40 on the wire and in the coil tower you can slide it in pretty easily.I usually put some silicone around the top of the coil where the wire goes in to keep moisture/dirt out.You can even slide a rubber boot over the wire and coil top.The NGK cable also uses a rubber boot style on the plug end which is better than the plastic caps found on some.

Usually a good pull will get the wire out of the coil but if you have a heat gun you may want to heat up where the wire goes in and it will help losen the glue they use from the factory.Just don,t go too crazy with the heat.