Your rear seat looks VERY similar to a w114/w115 rear seat. I don't know if they are identical, but they sure look it. So you might look into that for additional options. This website:
https://www.dieselmercedes.com/Mercedes_Rear_Seat_Cover_Kit_NEW_MBTex_Vinyl_W123_p/6120-W23.9-N.htm?gclid=EAIaIQobChMI5cTgyZr24gIVgrfsCh1n-A4NEAYYASABEgJp9vD_BwE
suggests they are the same and could be a source of the vinyl, but you would need to find someone local to install it.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).