I got mine from Greenstuffworld.com, a webshop based in spain. They are the only source for those I know of.
http://www.greenstuffworld.com/en/51-textured-rolling-pins
I have the "Aztec" and "Bricks" pins, my friend has the "Runic" and "Dark Runes" ones. Really cool!
The good thing about air-drying clays like "Fimo air basic" (be sure not to get regular fimo, that one is for the oven) is that they are not as bad for your health as Brownstuff/Greenstuff.
There is also a newish brand called "DAS" which seems to be even better I heard. Fimo is pretty hard (and thus brittle) when dried, I heard DAS stays a bit softer. The MSDS looks promising, as long as you don't eat it you're most likely fine.
MSDSs in case you are interested:
DAS
https://www.c2f.com/msds/DIX-DASAirHardeningClay.pdf
FIMO
http://www.dick-blick.com/msds/DBH_SDS_33284XXXX.pdf
EDIT: And we also tried it with GreenStuff and BrownStuff. It works fine on those, too. So if you prefer the epoxy stuff, no problem. The air-drying clays are cheaper though.
After use you have to clean it with water and a toothbrush so the texture stays like it is.