William: I think the method you settle on will depend on the final scale you select for the model. Model railroading sources are indeed probably your best bet.
But there are maybe cheaper alternatives. Posted below are some houses I built in 1:6 scale, for my little soldiers. The examples are stone, not brick, but the principle would be the same. I used styrofoam insulation board, and engraved the stonework with a pencil, then painted.
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[A gratuitous photo of the troops about to inspect the building:]
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It was tedious and boring, and would probably be even more so in a scale smaller than 1:6 (GI Joe-size), and insulation board would be too large. Maybe foam-core board would work.
Finally, a shot of a brick wall built using the same method.
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On the web, there is this source for printable bricks:
http://www.printmini.com/printables/wpf/bricksp.shtml
You could resize them to whatever you need.
Whatever you choose to do, good luck with your project.