Download the Mapsource file from the garmin website & save the download to say your c:drive. Use WinZip to extract the files & then run the file with the extension msi. This bypasses the search for an existing product.
This work around has worked for me in the pass.
Even though this may well install the Mapsource program it won't provide any mapping data. They are separate entities that work together. You will have an empty shell of a program if it runs at all.
TYRE won't open Garmin GDB files, though
ITN Converter will. However, there is an issue that might make this unwieldy. Garmin GDB files contain a large number navigation nodes for any given route, many times that as actually added when plotting the route. I'm talking in magnitudes of 30x as many. A day's route I have plotted for next years tour in the Vosges mountains has about 15 nodes that I added manually, the GDB file contains somewhere in the region of 420 nodes. Mapsource can cope with this without breaking into a sweat. Unfortunately ITN Converter and TYRE rely on the Google Mapping API and this will choke or grind to a halt with that many nodes.
If you can get whoever created the route to save it as a GPX file, Mapsource can do this using the 'Save As' command in the file menu, it will then only contain the user generated nodes and will open easily in both TYRE and ITN Converter.
It's possible that Mapsource installed without mapping will allow you to open the file and then save it as a GPX file which you can then open using either of the alternatives above. Maybe worth a try if you're really stuck but don't be surprised if Mapsource fails to start due to lack of mapping data.
If you want to get technical you might want to look at
OpenStreetMap options as
this can apparently be loaded into Mapsource... Maybe the Rosetta stone you're looking for?
