For better or worse, I'm duplicating their effort by putting every railbed that's ever existed into
http://OpenStreetMap.org. You can download an extract of the map in Garmin format and put it on your GPS receiver. Or you can just look at the map at that URL. Or if you have a smartphone, you can download the MapQuest app and choose the OpenStreetMap layer.
If you want to do interesting things, I can show you how to extract features from OpenStreetMap, like anything with railroad=abandoned and bridge=yes which will show you every abandoned RR bridge in all of New York State. There are over three hundred!