I have a Xbox 360 S with no power cords or power brick,where can I buy one

Between ebay and amazon you should find all you need just look arround

So many repeat answers,smh.

One thing you will want to be aware off is that if you buy a 3rd party power brick (not recommended) then you risk damaging your console.

Check out ebay and other online sites like that....or games stores around in your area.... could even check your local buy sell pages and pick up a complete 360 for cheap and use the supply from that.....

There are many stores, but remember to always buy from official stores, do not buy anything of dubious origin that could harm your console.

I would recommend, if you want to be safe, just buy official Microsoft products. I had bought a 3rd party set of cords and power brick years ago and the power brick did not work. It was a no-name brand and generic and there was no return policy for it.
It was cheap but still wound up being a waste of money. Just be safe and if you can, get the official licensed products.