The way I get Caches along a route:
Create the route you want to follow in Mapsource. Then from Mapsource, view the route in Google Earth. This loads Google Earth and highlights the route. Save this route as a .kml file. Then on the Groundspeak site, go to find caches along the route. This enables you to upload the .kml file you have created, and you can create a pocket query of all caches along the route.
(Search for gardenroute when on that page, and you will see the route I created form Mosselbay to Port Elizabeth)