Hub caps for 13" wheels

Hi folks. My 64 Plymouth still has the original 13" wheels and wheel covers. I'm looking for hub caps. Are they different from 14" or 15" ? I've tried everything from repainting the wheels to putting tape around the wheel cover retainers and still can't get rid of that annoying "Click/Creek" noise for more than 20 miles or so. It's embarrassing to say the least. Any help would be appreciated.
Thanks, Wally