Actually, I found one for $10 on Amazon
Union Electric Dogbone RV Power Adapter Cord Extension, 12 Inch 12AWG/3 Cord, 125/250V, for RV Moterhome, Boats & Trailers (15A Male to 30A Female, 12") https://www.amazon.com/dp/B07HDSHRWX/?tag=skimlinks_replacement-20