If I didn`t have some already I would buy some, or visit a garage and with a deposit ask to borrow their stamps,
letter / number stamps 5mm or 6mm will be ok, machine mart in I,o,w ?????
place trolley jack under car, with slab of hardwood in the area to be stamped, or the floor will cave-in
failing that, book it into mot garage requesting the stamping of your code prior to them testing it, its a 10 minute job ,