That is a great question. As an architect, when I am specifying materials for a project, I will weigh the green benefits with the manufacturing location. In comparing products, most product companies have websites that list their manufacturing locations, so you can find out exactly where a material is coming from.
Your area may also have a materials exchange website, or a Habitat for Humanity building supply re-sale store.
An architect, designer, or other green professional in your area would also be able to help.