I love shopping for stuff like this; in Seattle there are lots of good places but other cities have equivalents. Some places I would go:
1) Architectural salvage shops
- In Seattle my favorites are the Restore, Second Use, and Earthwise. If you do a search on Google for "Architectural salvage" +"your city" you will probably locate some near you.
- Habitat for Humanity operates Restores in various locations in the U.S. and Canada which you can locate via their website.
Not only can you find old windows at such places, but you can find old picture frames! In my experience they have a huge stockpile of old moldings and trim too which you could easily repurpose for frames with some miter cuts.
2) Surplus stores: by this I don't mean military surplus stores, but rather schools and the like who often have regular "surplus" sales open to the public.
- Public agencies can sell online via Public Surplus
- State & Local Government surplus stores are listed across the U.S. here; state universities are included in these listings
3) Flea markets and swap meets
- Flea market Mama offers an online swap & flea market directory for the U.S., while Openair Market Links provides information on markets across the world. You can also buy flea market & swap meet directory books or check them out from the library -- they're published by a variety of people and some focus on the U.S., some on Paris & London, etc.
3) Craig's List
- This is such a great resource; hopefully there is a local list for the area you live in. Click on the "for sale" category and then search for windows and see what you come up with. If you want to browse "for sale" categories, you might have some good luck in the "free" section, as contractors or people working on their homes are often looking to get rid of things like old windows. Its also great to read and search through the garage sale section.
Have fun finding some great stuff!