I’ve made a really good mesh for mountains, yet, I can’t find any textures/materials that do the part.

A lot of time what you think you are looking for in a texture is not what will give you the best results. Over the years I have seen some great mountain ranges textured with bark. I myself often use strange things for textures, for instance the the drum set on my web-site is a floor tile texture.

Don’t forget that you also do not need to use the entire jpeg when texturing. Sometimes adjusting the size can have drmatic effects. Adjust these with the min & max x & y settings in the texture buttons, as well as the repeat

You can find a to free texture links here

Hope this helps