If I have found no 9-square with words for all its diagonals, and needed place names to produce all-diagonal 8-squares, then 7-squares can be produced solely from the OED. Omitting place names reduced the crucial elements from 3386 reversible words and 878 palindromes, 584 reversible and 661 palindromes.
"All-Diagonal Seven-Squares From The Oed,"
Word Ways: Vol. 39
, Article 9.
Available at: https://digitalcommons.butler.edu/wordways/vol39/iss3/9