Where can I find a replacement hood for my 2007 Kia Optima

Do a google search - you'll see many options - explore all of them for best price. Keep in mind that a used hood of a different color will require MUCH more preparation work to get ready for painting - a new hood comes pre-primed and ready for painting right out of the box. Thus the new hood is usually the least expensive and recommended route to take > no hidden damage!