I assume you checked the bulbs again? It's not likely that bulbs on both sides would be out, but we always want to check the easy stuff first. I've had brand new bulbs that looked fine be bad, so I always test them for continuity unless it's obvious a filament is broken.
If you can read electrical schematics download the TW service manual (stickied on this forum) and see if you can trace the circuit to determine the most likely culprit. You can use a test light to check for juice at key points in the circuit. While you're at it look for broken or chafed wiring.
Since all the blinkers are affected I'm guessing it's either the switch or the flasher. Here's an earlier post about fixing the switch. If that doesn't work take your flasher to the auto parts store and have them match one up. I don't ordinarily like to throw parts at a problem, but flashers are not usually very expensive.
That's my 2 cents, maybe someone will post up with better advice.
Oh, one other thing. Does the headlight come on when you turn on the ignition switch? I notice my switch is getting a little finicky, and occasionally I have to wiggle it a little bit to get the headlight to come on. If I remember right the turn signals won't work if the headlight doesn't come on. Anyway, something to check. I hope you can find the problem without too much trouble.