Season's greetings

You may find a few 3D CAD models of Garmin products here:

https://www.google.com/url?sa=t&sour...mF4QJ1HHhczF-B

Definitely not a comprehensive variety of models.
Can't vouch for the accuracy, but they may be good enough to get you up and going, and I suggest that when you get serious about specific Garmin items then you can check the exact dimensions against the product ICD.

Hope this helps.