Have you check your local True Value/Ace/ or other local Hardware store. Many of these stores have small parts bins. Some more than others... Home Depot/Lowes are not that big on carrying small parts like your screw.
Mom and Pops hardware are...
Match the screw for that hole by the one on the opposite side of the aircraft.
The two screws that hold the detent mechanism in place are different from each other. Once you determine the needed screw, just put it in place and the clicking should...