I was just at the site
http://www8.garmin.com/support/downl...ils.jsp?id=209
and was able to start downloading the exe file of mapsource. This indicates it is still available. Try it and see how you go.

It does mention...
WARNING: This software will not work unless you already own a MapSource product. I don't remember how I managed to install it on my computers but I have it on 3 computers altogether. It may be that you may have problems unlocking your map on the program but it is possible to source free maps on the web which can be copied onto the memory card and used on the GPS and on mapsource software without the problems of unlocking maps. I found it a steep learning curve but well worth the effort.