"Losing spark" is a different scenario than not having voltage at the coil.

If there's no 12v(+) at the coil, then there's a bad wiring connection somewhere in the dozen or so connections between the battery(+) and the coil.

If the coil has voltage, but at times doesn't produce spark at the plugs, there are several things that could be the reason..... ECU, coil, power transistor, plug wires, distributor cap, rotor, distributor, wiring connections, etc. Since you've replaced most of these (how about the rotor?), that leaves the distributor, the ECU and associated wiring for both.

I'd replace the rotor (if it hasn't been replaced), cycle/clean the distributor harness connector at the firewall a few times. If that didn't work, I'd look for a distributor and ECU loaner to swap in and see if things improve.