You can download from below link. Please see instructions and pre-requisites below.
1. Download and extract the zip file to your local hard drive.
2. Execute the setup.exe from the extracted location.
3. If you are using Map Source, open it and navigate to main menu "View->Switch to Product" and select "SLMaster" or if you are using BaseCamp, navigate to main menu "Maps" and select the SLMaster map.
4. To install map to your device, please follow instruction given in corresponding software (Map Source or BaseCamp).
Garmin MapSource and Garmin BaseCamp both are trip planing software which can be used to communicate with the GPS device and install maps. However BaseCamp has some limitations such as re-installing a map to a device require manually deleting it from the device where as Map Source doesn't have that issue.