Wow, I do not recall the last time anyone mentioned these 'Outdoor GPS Games'. They were included on many of the Pre-Mass Storage devices, including the Geko, eTrex and GPSMap devices of the day. I am certain I have opened some of them out of curiosity, but I do not remember ever playing any of them.
When Garmin released the Colorado series in January of 2008, their first Mass Storage device, these Games were no longer included. Since the code for each of them is part of the device firmware, I doubt there is any real chance of copying them to newer devices. Even if someone where able to extract the ones and zeros from an older firmware image, they almost certainly would not work with modern device processors unless someone also crated a dedicated MAME interface just for that purpose.
Which game or games in particular did you enjoy playing?