I.S.O. Bertoia Diamond Full Cover  

I have a Knoll small bertoia diamond chair with a black leather seat pad which i am looking to replace with a full textile seat pad, but can't find one anywhere! knoll makes them and charges about $800, and i've seen some others on line for about $450, which is even more than i spent on the chair...local upholsterers won't do it without a pattern or a cushion they can tear apart. anyone know if a pattern exists for this or of somewhere i can find this that is more affordable?