It was actually ASM #14, but maybe Stan was thinking of ASM #10 because the Enforcers were in both issues.
Amazing Spider-Man Annual (Vol. 1) #3
Published: c. September, 1966?
Cover Date: November, 1966
“…To Become an Avenger!”
Writer: Stan Lee
Artist: John Romita and Don Heck
Inker: Mike Esposito
Letterer: Artie Simek