NORM - You mean a cover with the drawstring? They won't fit the higher back seats.
The little "U-channel" molding actually holds the cover material on the seat pan, the OEM seats use the cheap vinyl plastic cover material that bonds to the foam padding. So an upholstery shop will need to replace the foam padding & cover both.
Like Brian says, you could even do leather, or any color you want.
I used cheap fabric store naugahyde on the seat on my #72 and sewed the one seam needed on the wife's old sewing machine. The stitching was too close together and even though I double-stitched it the naugahyde ripped next to the stitching after about an hour.
Dad had the seat on the 129 re-done at an upholstry shop, they used better material and coarser stitching, but put too much foam rubber padding in and it ripped too, just took a lot longer.
If the seat pan has the drain holes in the bottom like my 982's seat does, that causes problems with the padding.
Recovering an existing seat could cost as much or even more than a whole new seat, but it should last longer. There's some really good materials available now. I bought a seat for my Super H 7 yrs ago made by K&M Seats, it's a replica of IH's "Tombstone" white seat they used on the high end 56-series Farmall, 756, 856, 1256, 1456. I paid $325 for the seat, almost as much as I paid for the #72 back in 1981, but that seat has 4 inches of foam padding on the bottom & back cushions, fold-down arm rests, looks great on the Super H. Wished we'd had a seat like that on it back in 1968 when I was running it all the time. Most comfortable seat I own, including my leather recliner in the house.