i know this question isnt about mercedes, but you guys are so smart about cars in general so i figured id ask

my grandfather has a 91 grand marquis. the airbag sensor light continously flashs. the code it sends says its a fault in the drivers airbag, but the dealer said it was a fault in the airbag sensor relay, but that the airbag was fine. when he inquired about it, they said that ford nor anyone else makes the part anymore (pretty much telling him to deal with it). he didnt believe it, and neither did i, as i can get new parts for my 76 mercedes! anyways he asked me to look online to see if I could find the part. would anyone know where it could be obtained?

91 grand marquis air bag sensor

the part # they gave him: 718AZ-14B004-A

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76 300D 108,110 miles
99 Saturn sl1 80,000 miles - moms
91 Grand Marquis 45,000 miles - Grandparents
97 Ford F150 - 16,000 miles - Grandparents
73 Ford Monarch (parked 65,000 miles - Grandparents