I bought the material for my 67 300 from SMS in Oregon. Last year the price was $79 yd for the factory pearl white vinyl. The seat foam had to be made by hand by the upholsterer. There are no pre made covers or foam available for this model.
The guy I used charged $900 to make new seat covers and foam for the bottoms of both front buckets. I supplied 3 yards of vinyl.
Eric