... I'm looking for software by the late Alex to convert maps from .img format to kmz (img2kmz).

Thanks.

late searches are denying img2kmz.exe as malware - may be Garmin push on Digital Rights and Licensing to Google - to deny searches like this.
Most best you could get to use GMapTool + cGPSmapper , and then use QGIS to design map and export with GarminCustomMap plugin to export a valid .KMZ file.
Tho Garmin has limited CustomMAP to max 100 tiles (one tile = 1024x1024 pixels) - limiting area u can see in very detailed perspective.