There are some useful workarounds to the problem with maximun map size of 2GB with older gps units.
As for the 60csx, which supports only one map file (gmapsupp.img), you can use a larger sd card and have several .img files if you have access to a pc or smartphone. Then you can rename the file you want to use to gmapsupp.img and the other file(s) to something more descriptive.
If you do not have access to computer you are left to having several sd cards and switch cards.