I think the divide-and-conquor rules apply here, in other words, rather than suspect all of the car's electrics you should disconnect/isolate large portions until the problem goes away and start homing-in.

Here's a few suggestions, some based upon Vauxhall experience:

I think the front to rear wiring has a connector in the NS footwell side kick panel. Disconnecting this _should_ stop the rear lamps working and therefore eliminate the rear wiring.

One common indicator/headlamp connection area is the steering column stalk controls - maybe something's up there?

Usually in the fuse area there are relays: You should have headlamp (or at least a hi/lo beam) relay and an indicator relay - unplugging one of these might help narrow the cause.

Sometimes (I think) the hazard lamps work from a separate relay, although the wiring is common to the lamps removing the hazard relay might give you a clue.

Re-reading this I'm mindful that I've assumed that you need to operate the headlamps/indicators for the fuses to blow, is that actually true? Maybe you could elaborate a little on what you have to do to get the fuses to blow?