Try this link for their homepage:
https://alknochinteriors.com/Check their 'Camaro' page for seat foams and springs (?)! I don't see much else for our Buicks?
Sale is from March 25 to April 15, 15% off.
I recently purchased a pair of seat foams for my '66 (different than '65) from Thornton Reproductions.
These are supposedly made by the oem supplier. They're not 'extra firm' like the PUI foams, and less expensive than the ACI foams which are often recommended. I'm happy with the Thornton foams and would certainly recommend them for 66-7 seats.