Likely the only source would be SMS Auto Fabrics in Oregon. They have new old stock material and would custom make them to exactly match your originals. Expect to pay a hefty price and wait at least a year (or so) to get them though. smsautofabrics.com/
I don't have knowledge of the 1971 trim codes but it could be found in a Master Parts Catalogue for '71 or an original Paint & Interiors booklet that the dealer would give out to customers when deciding how to order a new car.
As for the "59", that is probably referring to the body style, however the only valid ones for a '71 Catalina are: 69 (4-door sedan), 39 (4-door pillarless hardtop), 57 (2-door hardtop) & 67 (convertible).
It might be worthwhile to see what a local upholstery shop can get you. You might get something reasonably close for a lot cheaper. That generation of full-size models used full foam construction for the seats and it compresses significantly when you sit on it, stressing the upholstery & seams, causing them to split.
