All the artists are free to use them as they wish in the program, but don't claim the set is made by you!
I have this posted on my tumblr too - my tumblr.
And here is the link where you can go and download the set - P.T.S - blotmap & brushtex set V .
set © M.C
It's just the way you save those textured images - as for in this case as a bitmap file and you put it in the blotmap folder.
As where you can find them, just search textures (example of texture grunge or paper, or metal and so on) on google.