We have a large collection of maps as many areas where we live and visit do not have cell access...thusly no access to Google maps on the smartphone. All these maps shown here are kept in the bag (which has many more maps in it) and are taken on every long distance out of town trip. The white maps are old forestry maps and are almost collectibles as they show old roads/trails that are not on newer maps.
Based on our experiences, the best places (and in no certain order) to get free maps:
Tourist info offices
Chamber of Commerce offices
CO's (conservation Officers)...Yes, some here may have the odd map that they will hand out if asked.
Forestry offices
Sporting / Outdoors / RV shows...Many areas of the country are eager for visitors and often have free maps to hand out
Local Real Estate offices
Google Maps / Google Earth. Print them off beforehand.