I bought them from fordemblem.com You can find them a bit cheaper on ebay, but by the time you buy them all you will have the same amount in them as I do. I paid like $115 for the powerstroke badges, F-350 lariat badges, and the tailgate F-350 badge. That was shipped to my door. They were here in 4 days after I ordered. Very fast shipping. Hope this helps.
Also if you are taking old ones off, look into buying a pinstripe removal wheel for a drill. It saves you a lot of time when getting the old glue off.