The only place an assembled seat cushion would exist is at the respective assy plant. There MIGHT be a genuine Chry part number for the assy, BUT they were all built-to-order per the Broadcast Sheet. There were trim codes (colors and fabrics) that would define the seat, though.
IF a seat needed repairs (warranty or otherwise), the car went to a very good upholstery shop for repairs. When done, the repairs were not detectable, as a general rule. There were also factory part numbers on the fabrics used on the seats, but the items were procured by the trim shop via their supply channels for the factory items. OEM dealers did NOT stock those upholstery items as once ordered, not returnable. So the upholstery shop got the needed items through their supply chains. Usually "DeLeo" or "Detroit" sample/swatch books (and the relatged supply chains involved).
From the pattern in the cloth, I would suspect it would be from a middle 1960s vehicle. Is the vinyl dirty or is the seat all fabric? Or both?
At
www.hamtranck-historical.com (might have to manually input that address), in the Color and Trim Guides, in the "Library" section, there are graphics of each seat style available for cars of a particular model year. Similar to the ones in the Interior section of the appropriate model year Chrysler Parts Manual.
Just some thoughts and observations,
CBODY67
