The last time I redid my AA-1B seats was in the late ’80’s. Back then you could still get factory surplus upholstery sets.
Today, the first place to look would be Airtex interiors. I did a complete Airtex interior for my Cessna last winter. These kits provide everything needed. You strip the seats down to the metal frame and build them back up with new sling material, per-cut foam and new covers.
The kit price for the basic materials for the AA-1 seats shows to be $726, and goes up with better cloth or leather. They also make side panels and carpets.
Other options would include taking the seats down to a local Auto upholstery shop. Remember that the FAA requires a Burn Certification on any materials used. An owner can sign the logbook for seat upholstery installation as long as it does not require the disassembly of any structures. which it does not in an AA-1.
Good luck with this project!