Where to download 4 band NAIP imagery?

To acquire NAIP for Oregon that includes the NIR band you must contact the OGEO office directly (gisgis.state.or.us or 503-378-2166). The NIR is not available on the download site.

When you refer to "historic" NAIP including the NIR band you are going to be somewhat out of luck. Many states still do not include NIR in their contracts and the USDA-APFO option of a NIR band was not officially added to the contract template, as part of NAIP, until 2009. To acquire this data you will have to go state by state. Colorado has an ftp site that you can download the current, quad-level, NAIP that includes the NIR.

I do not believe that Oregon added NIR until the last acquisition of NAIP, but there could be one additional year that includes NIR. For current NAIP (RGB only) for all states, APFO has a webmap service that can be added as a "GIS Server" in ArcGIS (http://gis.apfo.usda.gov/arcgis/services).

See http://www.oregon.gov/DAS/CIO/GEO/pages/data/doq.aspx for some historical imagery. Google will find it for you and no doubt more by simply searching on Oregon GIS.

The NAIP program only does part of the country in any particular year, and of that only a small amount may be in 4 band or even 1m resolution. See http://www.fsa.usda.gov/FSA/apfoapp?area=home&subject=prog&topic=nai which has lots of information on the program and even a map showing NAIP coverages from 2003-12. Bing maps and Google Earth often make use of NAIP imagery and have historical layers.