With the release of Substance Designer 4.4 Allegorithmic has included 50 Substances from GameTextures.com which you may have missed.
Unfortunately they didn’t seem to make it very clear, I only found out about it from one of the demonstration videos, and even then I missed it the first time I looked. To get the textures and they are pretty nice you need to go to your account page and select the Substance Designer download option and look in the list for the two zip files. As of this article they should be number 2 and 3 in the list as shown below.
Be sure to check the Substance Designer videos on youtube as you never know what you may miss, perhaps they mentioned in some obscure release note but I failed to see it. Worth noting they are promising to add more Substances with each release, which is nice to know.