If you've got a good spark from the coil, but not on the spark plug leads, it pretty much narrows it down to a few suspects:
1) The distributor cap: These can develop fine cracks that fill with moisture and redirect sparks from where you want them to go.
2) The rotor: it just redirects the spark from the center coil lead to the appropriate spark terminal. It can be oriented wrong, busted, etc.
3) The spark plug wires: They can short and let the spark go somewhere else.

Personally, I've had more issues with distributor caps in the past than with rotors. And usually in damper weather, too.
--
'63 PV544 rat rod, '93 Classic 245 + turbo