Place ads offering the windows for sale in local classified ads, such as newspapers and online sites such as Craigslist. List the sizes of the windows you offer, along with the brands. Also, state whether or not you offer installation.
Go door to door in local subdivisions and neighborhoods to try to sell the windows. Avoid asking the homeowners yes-or-no questions. Focus on older homes that might need remodeling.
Team up with local contractors in your area to offer your services together. If you can find a contractor that installs windows, you can work together. Ask friends and family for information on local contractors, or visit local construction sites to meet contractors.