A free and good map that shows many of Galbraith's trails is available at galbraithMt.com.
All Galbraith maps share two fundamental problems: one is that there are few landmarks on Galbraith so it is difficult to know where you are on the map. Second, the trails change frequently so the maps become outdated quickly. However, they are better than nothing.
A good option is to join a WHIMPS ride (Whimpsmtb.com). Alternatively, just ride around and watch were other riders are going. They will be happy to give directions.