Here is a site that you might be interested in for either a counter balance support or a system of steel rail supports. I think these are intended for either 2cm or 3 cm stones, but you can call the company to get more details.

http://chemical-concepts.com/CounterBalance.htm

Counterbalance is a cool system: I wish I'd seen that before my granite went in.

But since I didn't,I ended up using regular bookshelf style end brackets, painted to match my other hardware. They'll blend in well when the oak cladding on the island gets stained, but I'm at that point where things are functional enough that I'm having a hard time sprinting to the finish.

Since these brackets don't hold huge amount of weight, I used a lot of them: 8 on an island where the cab iself is about 24x52 with a 12 inch overhang on 3 sides.

No pix of the actual construction, but our builder put in two flat steel rails at each end of the 4-foot x 12-inch-deep overhang. The rails are attached to the tops of the cabinets beneath the island, as well as to some reinforcing plywood between the cabinets. Then the plywood underlayment for the granite was bolted to the steel rails. You don't see anything unless you lie on the floor and look up at the underside of the overhang.

You can buy corbels from places like enkeboll. Here is our island:

Here is a link that might be useful: corbels