You can obtain free electronic charts from the National Ocean Service (NOS) section of the National Oceanic and Atmospheric Administation (NOAA) web site. The NOAA Raster Navigational Charts (NOAA RNC®) are compatible with the charting software provided with America's Boating Course 3rd Edition and many other charting programs. Just click the NOAA link, and follow the instructions there to download the chart(s) you need.
If you want to view the charts before downloading them, charts can be viewed and downloaded by using the NOAA Chart Viewer. This is easy to use and allows you to view the chart of interest and download it from the same page. Use the Chart Viewer for U.S. Waters or the Chart Viewer for Global Chart Coverage as needed.