This bridle fit my percheron. Just get the oversized one, obviously. It's pretty cheap too, but I've shown in it and pinned, so it's pretty good.
Kincade Fancy Stitched Bridle w/Reins - Bridles - English
You should be able to buy a nylon western bridle and adjust it to the loosest holes. You'll probably have to take the browband and throatlatch off like I did, though.