Maps of Heavily sprayed areas in Vietnam. You can download a file and Use the Google Earth map.
Maps of Heavily Sprayed Areas and Dioxin Hot Spots - The Aspen Institute
Along with the C123's, Small aircraft, fighters, helicopters and some boats were used to spray.
Also found the use of ground vehicles with mounted sprayers and 2 gallon field pack sprayers for manual application.
Some US Cities bought surplus sprayers that they used to spray for mosquitoes, remember DDT? Along with Dioxin, DDT was extensively used.
Post War use of the Planes:
"Many of the same aircraft that dispersed Agent Orange during the war were later used as transport vehicles during (relative) peacetime, primarily between the years 1971 and 1982. And tests taken many years after those transports show the planes still contained dangerous levels of the chemical."
More Here:
Did Agent Orange Poison US Military As It Did Vietnamese? Yes - Flashbak