An excellent resource for finding nitrogen tire filling stations is Getnitrogen.org, which lists nitrogen filling stations near you after you input your ZIP code. Another helpful site that requires only a ZIP code prompt is Nitrofill.com.
On the right-hand side of the main Getnitrogen.com page, find a Nitrogen Locator box, which requests your ZIP code. After providing a ZIP code, hit the Search key and a list of locations within 100 miles of your ZIP code appears. Locations are differentiated as to whether you need to purchase tires or have a membership to get nitrogen, whether they are truck friendly, or if they are a delivery-only option. Nitrofill.com offers more general information, providing only locations of Nitrofill authorized dealers.