You've got 2 possible sources that I know of for A-7 gear. Ed Dobias of RC Crafters makes the scale gear for the Jet Hangar Hobbies A-7. He has a post in the "Scale F-18 gear" thread here in the Jets forum. Contact him to see if he might be able to make a larger version for you.
The other possibility is Century Jet Models. They are close to releasing their own large scale A-7. I'm not sure of the scale, but the gear may work or they could be enlarged for your needs.

Good luck!

Tom