If there is a Lowes close by, you might try their hardware section and see if you have any better luck than at Home Depot. Your local hardware store could be another source you might also try. A local ACE hardware store has surprised me more than once when looking for hardware for some special projects.
The fastener you need, Ford called "Hex Washer Head Self Tapping Screw." The Ford part# is 55981-S2 and is 1/4-14 X 1/2". Although a few dealers may still have small inventories, these are no longer available from Ford.
If you don't find anything locally, AMK sells a version of this screw but has a $30.00 minimum order with a $10.00 shipping charge. Not friendly to your finances unless needing additional hardware.
National Parts Depot (NPD) sells a version of this screw, but the application they list for it will throw you off a little. Ford used the same screw on the Fox Mustangs to attach a bracket to the hood latch that retained the hood release cable and the dust boot for the clutch fork on the 5.0 models.
https://www.npdlink.com/product/scr...search_terms=55981-SB&top_parent=150000&year=