I honestly have no idea what happened to my desert tileset... it just sort of phased out of existance, I might try and find it on my hard drive though.
For the speed, it's probably just how XP animates it (it's editted from the waterfall autotile), but you could change the speed with a script such as poccil's tilemap rewrite.
A source? Do you mean who created it, or a source as in the source of a river?
If the first, I made it; if the second, then it should run straight off a normal sand tile, I'm not sure how else to do it. (Desert cliffs, for example).