I live in a predominately rural area, with farmers & boatbuilders and such. We have a killer local hardware store, one of those dusty dark places that has two whole WalMart-sized shelves of nothing but fasteners of all sorts, for people to build stuff with. Living out where you do, there's just got to be one of those stores somewhere, it's not the "Ace" for sure. Ask the guy on a tractor.... ask Warmoth where they go to maintain their machines?
Aren't "P90" screws the same thing as Fender bass pickup screws, #4 X1.25"? Everybody and their dog has them. Another good way to tell you've found the right hardware store is that they order you anything under the sun, like wax-free denatured shellac and stuff. Even at full retail at a hardware store, what you save on shipping charges buying everything over the net can add way, way up.
http://shop.ebay.com/?_from=R40&_trksid=p3984.m570.l1313&_nkw=fender+bass+pickup+screws&_sacat=See-All-Categories
DiMarzio makes them in all the colors, so any DiMarzio dealer.... arf.