Does anybody know a site that has OSM maps of Switzerland that I can install in MapSource, to put in my Venture HC?
The site mentioned on the wiki of Kowoma only has a full .img file, but my Venture has limited memory. 
Here is a big list of Garmin map providers. You can use http://garmin.na1400.info/routable.php to generate a map for Switzerland.
Thanks! I missed that the routable also provides MapSource installation. Beginner mistake 
It works very well.
Great! You’re welcome 