http://mytopo.com/ is where I have gotten some.
For training I sometimes make my own to purpose out of poster board. It lets me put what I need where I need it to be. I can make the squares bigger and terrain features exactly how I need them to aid in visuals.
I have also made large grid square protractors out of plexiglass to fit my hand made maps.
Sometimes getting people that have never done map reading to understand on a map full of terrain and made made stuff can be difficult. This all lets me control what they actually see and do. Once they get it we move on to real maps.