NAPA auto parts will have copper-core spark plug wires for you (I bought a set there recently).
As far as the miss - could be something to do with the governor kicking in and adding fuel to the mix - perhaps a main jet obstruction (or not since you've cleaned it out) or maybe the governor's kicking in too far or not far enough. Just sounds like you have problems when the governor opens the carb up.
Could be a bad spark plug out of the box (I've had that happen) - try a set of Autolite 295's if you don't already have them. You might also try setting the plug gap to 0.030" (the manual calls for between 0.030 to 0.040).
Is the miss regular? Does it seem to be on one cylinder only? Might be something to do with valve seating if it's not ignition related.
I'm sure there's something (or many things) I've left out.