"Ordnances" -- with no "i" -- would have been the right word. I think that most people who see the word "ordnance" think it's misspelled, and that it should really be "ordinance." Actually, "ordnance" can be a properly spelled word.
Sometimes "ordnance" is improperly corrected by adding an "i." Sometimes "ordinance" has to be corrected by eliminating its "i."
- An ordinance is a law or other government regulation.
- Ordnance is something that goes boom, like a cannon or a bomb.
- An ordinance can deal with ordnance.