Are you sure it is spark?
If you know it's spark then its easy! There are only a few things in the chain, just test them one at a time. I think you mentioned somewhere that the coil has been checked. So next is the coil-dizzy lead (replace it if there is any doubt). Then the dizzy cap (inspect the points, replace if necessary). There is the dizzy itself, but for the moment just hope that is ok and try all the rest (unless you have a spare). Plug leads (if they look old replace them). And plugs (check for correct gaps, if old then replace).
After that try replacing the dizzy if there is still a problem, but i would say 90% of all your potential spark problems are listed there.
There is also the main relay (covered in the INFOBASE). It doesnt sound like that is at fault, but it doesnt take mych to check so you could do that too.
If it STILL doesnt work post here again and we can all have fun playing "Guess the fault" ;D
Have fun
:-X ???
That way you can get it out of the way.