I found this site for downloading GPX files. for Pennsylvania hiking trails. I saw somewhere on this site somebody looking for trails to load. I am not sure if these can be sent to a gps or not.
http://www.pahikes.com/search.aspx?q=GPS+trail+download&search=Search
Those look like .gpx files. You should be able to load them in Mapsource, then send them to your GPS as tracks. You could also import them into Globalmapper or other programs and turn them into "trails" on a map.