1974 Mercury 500 50hp outboard plug wires?

I have a 1974 (SN 3823085) 50 HP merc. 500 model.
I'm having trouble with the plug wires arching on the engine. I have removed the wires and double insulated them with heat shrink and electrical tape and I'm still seeing sparks from the wires. I want to replace the wires but I can't seem to find them on line except for wire kits. Any suggestions on who would have the wires and also the coil wire for this engine?

James
September 2009