Check with Katzskin (I believe that's how you spell it) in California. They may sell a replacement kit that will work. I put their leather kit for my 1999 Dodge Ram pickup in my truck in January 2001, and the leather still looks and feels great. At that time the Ram kit sold for about $700, and it requires more leather than an XK8 would. No idea what the same Ram kit would sell for today....
2005 S-Type 3.0, Quartz / Dove
2006 XK8 Victory Edition Convertible, Onyx / Cashmere
Raleigh, North Carolina
I recently re-covered my '01 XKR drivers side seat cover. I used GAHH Automotive, North Hollywood, CA to make the seat cover and ship to my installer. The cost was $572, plus $178 for the installation. The leather matches perfectly with the backrest that remains original. I have attached pictures of the seat cover installed and the seat cover removed. I am planning on selling the old seat cover, just has minor wrinkles in the leather, no discoloration or tears. Send me a PM if you are interested. I was very happy with the delivery and quality. I am going to use them for the fabric replacement on the A pillar too.
1966 XKE Coupe
2001 XKR Coupe, 2013 JCNA Championship Award-2nd Place
2004 XJ8 Sedan