My rear springs need the plate that they sit on.

My 1991 new yorker salon is in great condition. low mileage too. Had it undercoated, but the salt prevails here in western ny.  Rear spring fell out due to the rust rot of the spring plate or cup on the axle. Having a difficult time finding replacement parts or even a full axle. Hate to scrap a beautiful car due to the lack of parts. The car has too much character to walk away from. Thanks to all who can help with ideas and info.