This request seems like a very long shot but worth a try
A new set of mats if you can find what you need should be the way to go to accomplish what you are trying to accomplish
I advised Jason where I indeed found a set of rubber reproduction aqua floor mats considerably cheaper to the tune of right at $175.00 cheaper than the most expensive vendor which we all know. I'm not sure if I should throw vendor names out here on this forum or not. If so I'll be happy to disclose my findings.
Can you tell me the vendor you spoke to about the mats ?
Try putting it out there on the Cadillac lasalle club web site ,i found a set of rear factory mats somebody had that were perfect for my 64 , good luck hunting….