The disc would be worth MORE if there was LESS of it....8' and under sells better. Anyone wanting larger disc would likely want a heavier model. Deere disc's of that era weren't extremely popular outside of died in the wool Deere-a-holics. They tended to ridge more than other brands. IH disc's of that era were by far and a way better.
I could probably round up a half dozen or so of those Deere disc's here locally, 10' to 14', under $500 each, and before lunch time.