The Website that azalea mentioned is a great resource for user-created Garmin maps. They also have a tutorial on how to load Mapsource if it didn't come with your GPS:   (You need to Login or Register. Many of the user-created topos are better quality than what Garmin sells. But, you do need Mapsource to load them. So, follow the tutorial and you should be fine.

Also, if you search around you should be able to find a GPX with all of the BW campsites and portages listed.