Where do I find genius mechanics for my F1 style pit stops?

First, we have to dispel the notion of what level of mechanical work is going to happen. Service stops are usually 10 to 20 minutes. So transmission rebuilds or cracking open engines, that's out. Swapping a half shaft, ok, replacing an A arm, ok, those are doable. But mostly you're going to need some regular guys with some amount of mechanical knowledge. If you had a couple guys who could jack up the car, swap some wheels, torque them properly, and knew how to change brake pads, you would make out just fine, because that's what most of the other teams have.

The first source is obvious, it's your friends. The second source, more difficult for a first time rally crew, is sharing some crew guys with another team. Since the services are limited in time, if you have one faster car near the front of the pack and one slower car near the rear of the pack, the times that they are in service doesn't overlap. The third source is to find some guys from your favorite car forum that live relatively near the area. Start a thread asking for crew in the local sub-forum. Generally, you'll offer food and a roof over their head for the weekend in exchange.

The other ancillary tasks of your service crew are basic errands, transport, cleaning, and food prep. Someone has to go down to Walmart to buy that tarp you forgot to bring. Someone has to drive the service vehicle over to the service area. Someone has to clean the mud off the windshield so you can see. Someone has to make those peanut butter and jelly sandwiches you're going to grab just before you leave service to eat on the transit to the next stage. So don't overlook the benefits of having someone on your crew who isn't a mechanical person at all.