I do suggest the modeltrain-terrain-sellers as well. I dunno if these are international, but NOCH and Busch seems to be very good, though I think each country does have their own good manufacturers. And do not hesitate to buy a light green here and a dark green there, etc.
Though they are usually pretty much the same all over, it may still vary, so have a look at all, and choose the most fitting colour for Your project.
If You are not in for a table with lots of different hight build in, then do not do too much "stuff" like branches and stones directly on the table, but keep them on the modulars. Too much branches glued on here and there and You cannot put modules on these areas. Tricky with scatter-rules.