It could be possible, but unless they can prove the procedure and documents required to have it an approved part it would be against the regulations and company policy.
If the aircraft lists these screws as locally obtained under a part number or supplier it is perfectly ok, I doubt it does!!
Again refer to the parts manual from the manufacturer for the part number or any alternate if the local hardware shop can match then it may be possible to use them (I said MAY!)
Simply ask them to refer the approved data for the screws use in the paperwork that requires certification. Or report them to FAA if they refuse.