Also there are other buildings that produce orc's. Craftable in the academy is the Orc's Nest, and also the AW Heroes Forge. On top of that several expiring buildings can give them if you win one in the spire or an event, Genie for example.
Orc's are a commodity like coins, supplies etc and not to be confused with the Orc style troops that can be made in the Training grounds using Orcs, the Orc Warrior and Strategist