Sounds most definitely heat related. You probably already know this but heat increases resistance, resistance can fault a component or wiring to the point that you lose spark. Have you noticed does it do it quicker on hotter days.
You can improvise on testing procedure eprov recommended. Make sure the bike starts, has spark. Pick a component, heat it up, fire the bike up, turn it off, move to the next one.....
I friggen hate going through electrical test procedures personally.