Have you contacted Impulse? Perhaps their customer service can help. Although according to Nike-It that download should have the texture packs in it. The best bet is to contact Impulse's customer service and let them know part of the game is missing from the download and let them know you *want* all the files that go with the game.

I think I'm going to download the game directly from 1C instead of anywhere else. If any download will have the correct files with it, it will be the company that made the game.

From my understanding the whole sourcemedia directory is 10.9 GiB, and of these proper textures take only like 400 MiB. The rest is 10.5 GiB folder named "in-progress", which contains uncompressed DDS files, with layout info, for game campaigns. These files are not necessary to create your own campaign at all. They are needed for editing original campaings. And for editing/modifying only - not for viewing, because viewing is possible without the whole big directory at all, the data (including textures) is taken directly from game files then. I don't know why aren't they compressed in this steam distribution. Please someone correct me if I'm wrong.