Home Depot, Lowes, any hardware store really. Get the 3M Brand. Look for a good strong adhesive. Ask the attendants or what not. Then before you tape the plate. Clean the back of the plate and the surface area you're going to mount. Wipe down the area with full strength Alcohal (Johnny Walker works best, JK. Any Isopropyl Alcohal will work). Lube the area with some dilluted dawn soap and water. Begin to apply the plate. Position it how you want it. then firmly begin to press the plate against the surface of the paint. Hold it there for a couple of minutes. Then let it dry for 3-4 hours. A hair dryer will spead the process and help the soap dry. Wax the areas the alcohal and dilluted soap came in contact with.
My explanation sounds rather difficult but its really easy. I used the same method to apply the bonnet stripes on my old mini cooper and to mount the front euro plate on my cousin's BRONCO (yes I know,

, to each his own).