All you have to do is find and buy SATA cable somewhere, like in an internet-shop, or a nearest hardware store.
Usually, several SATA cables come with your motherboard, if you bought it in a Retail (Full) package. Sometimes SATA cables also come with PSUs in, again, Retail package.
If you bought your motherboard as a second-hand from internet-auction sites like "e-bay" or "Craig's list", then you probably didn't have any additional (or any at all) SATA cables with board itself. Thus, you should buy them by yourself.
What is your country/region? Maybe I can recommend a couple of local stores where you can easily buy those cables.