Welcome to the community!
There is a Fido kiosk located in Terminal 1 at Pearson Airport (see here). Alternatively, you could also have the SIM shipped to your address in Canada (see here). You should note that the new SIM card would not yet be associated with your account. That's why anyone can purchase a SIM from a store. Once received, you would need to update your SIM card to the new one. Since your old SIM is lost, you would need to contact customer service to update your SIM. In addition, they can also be contacted via Live Chat, Facebook, or Twitter. Those methods can be accessed via the contact page posted above.
Hope this helps 😀