I had to do similar research and work a few years ago, albeit not for an airport or anything to do with aviation. I did, however, find the following useful:
- Archives - private, museum, and government-run archives are great sources for old photos and their proofs are usually well-kept, too.
- Newspapers - find newspapers that would have been around during the opening/construction of the airfield. Most likely they would have photographed and/or covered the opening and construction progress.
- Local stakeholders and families will quite often have photos of the area from when they were young or if they had a financial interest in the land. These were typically the most difficult sources of photographs as people are reluctant to share what they have and then they want WAY too much money to sell.
For an airport, I would also be inclined to call the Department of National Defence, as they would have had photos of the airport over the years for their training etc purposes.
You could also get in touch with the various provincial and federal heritage and historical minitstries/agencies to see what they can provide.
You should consider trying the Hamilton Archives at Hamilton Central Library downtown at Jackson Sq. They've got lots of Hamilton history pictures and would most likely have a bunch of the airport. If they don't, they might be able to point you in a good direction of where else to look.