There is a place out of the Netherlands that ships to the us, if it is still around. I paid around 300 for 4 square meters. Plenty to do the entire car plus some. The transaction involved a bank transfer. Let me see if I can find that information. I found the company from the Pelican Porsche forum. the oTher thing is they were selling out of a lot of the older styles so its a maybe. Its a fraction of the cost as Cabrio.de or one of the other high end places from De, forgot the name.
Edit, Here
https://westtrading.nl/en/car-upholstery/seat-upholstery/brand/mercedes/
They have some of the classic colors left still. Make up a business name when addressing them. Shouldn't be an issue. Mine came very quickly. I was worried about the transfer, but it went well. Had to pay customs.$25 or 50 I can't remember.