I found this site, not so you can buy their stuff but to give you some ideas. They seem to think it is all for kids but we adults fidget too!
http://www.therapyshoppe.com/product.php?cat=7
Thanks for this link, Renaeden. We already have a lot of things like the ones that they sell, but it is fun to see more.
I'm kind of lucky because I have a daughter, so I can buy whatever I think that she will like to fidget with and then I get to play with it too.
She loves these magnetic stones:
She likes this play foam, especially while driving to school:
I give her two colors at the same time and she tries to mix them as uniformly as possible, then we make different shapes with it, like multi-colored snowmen or whatever.
She also likes Silly Putty, which is part of this kit.