Also check the wires between the points and coil, coil to switch, switch, switch to battery. Intermittant problems are a biatch to track down. When it's doing it (no spark), try hotwiring the coil and see if you get spark, That eliminates half your circuit right there.
Points and a condensor are about as simple a system as there is. A few jumper wires and that's about all you need to diagnose it. I used to use 6 cylinder Chevy parts. Every auto parts store carries them.