I was looking at websites and remembered you saying your child likes slinkies and smoothe things. I found these that are smooth, plastic springs called Spridgets at http://www.autismshop.com/games-playthi ... idget.html
I can imagine that pulling one of these through my fingers to feel the bumps would be nice for me. But I don't know what your son does with Slinkies; I imagine the motion and the sound is what he is after with a metal Slinky. These Spridgets may not be something he'd get anything out of.
Something I have is a cat toy from Walmart. A friend of mine had one when i was staying at her place while visiting out of town so I discovered it quite by accident. It is a stick with brown feathers and an elastic cord of brown and beige twisted around each other. On the end of the cord is a squeaky mouse which sounds more like an overly happy bird. I came home from church there seriously overstimulated and overwhelmed and picked it up. It was awesome. I hold the stick part in my right hand and shake it, and the mouse held still in the left hand. The spiraled cord makes stripes in the air while the mouse squeaks. Gets visual, sound, and motion, while rocking foot to foot or pacing in circles. A cat toy! Should have known. So I found one and bought it the other day. I do share it with my cats; I hope they are grateful. My kids like to use it with the cats too.
Another thing is those silicone (I don't think they are latex; they don't feel, taste, or smell like latex) pencil grips you can find pretty much anywhere office supplies are sold. They make quiet, soft, sticking sounds when you unpinch them or pull and unpinch them. They bounce nicely. Mine are transparent, different colors with glitter in them with different textures on the outside which make for tactile and visual comfort. They are nice to chew on sometimes. Only thing is, they are not attached to any cords and wouldn't be strong enough to stay attached to a cord so you have to be careful of chewing them and not forget what you are doing: choking hazard there I would say. You could also string them onto a cord and chew them that way or swing them like a jump rope. I swipe them together for the sound and vibration too.
Edited for typos.