I have used maps from these other sources too, in addition to the "Free worldwide ..." link already posted:
GPSFileDepot - maps4gps's Garmin Compatible Maps
Europe - OpenFietsMap
I am not sure, but I might have also used this one:
https://www.openmapchest.org/
I usually use a vintage GPS with black and white screen and very long battery life with screen on full time, but if I need more memory I use a Garmin 62S with an extra memory card installed, but I have to have the screen set to time out very fast to avoid burning up the batteries in the 62S.