I have mapped a lot of rivers and streams in Nepal the last week. I saw that most of the existing rivers and streams don’t have a name.
Maybe the following maps can be usefull : http://www.lib.utexas.edu/maps/ams/india/
Nepal is included. The maps are from about 1955; that means no license problems.
Perhaps local mappers can check, if the maps are usefull.
I looked at those map. I think the map can provide good information about the names of the rivers and streams as you said and for other information as well like place name, roads, boundaries. Thank you for sharing.