They're actually a specialized stud with wood screw threads on the half that screws into the wing stand, and machine threads on the half that goes through to the under side of the decklid. The two halves are separated by an integral washer welded on. I've searched in the P22 (illustrated parts manual) for the specs on it but it's not listed. I doubt you'll find anything
exactly like it at the hardware store, though there are plenty of these dual thread studs available in sizes that will work. Just make sure that the part that screws into the plastic (coarse threads) isn't any larger in diameter than the original ones or you'll end up breaking the rather brittle plastic in the wing stands as you screw it in.