I realize it's an odd way to start mapping, but I am actually making a hieghtmap to import into a game. I am doing it in photoshop atm and am using a lite-weight program called WorldPainter (made for the game im using it for) to further modify it, however, 95% of the terrain editing will be through the heightmap.

here is a sort of render:

Does anyone have any mountain brushes? So far, All i am doing it using the render difference cloud technique, adjusting the levels and setting the layer to screen. Also am copy and pasting real mountains from other heightmaps.
Lastely, does anyone know a good way to make sand in heightmaps? Currently, I am copy and pasting this :

where i need sand and lowering the opacity as need be.

thanks for all the help