I honestly doubt you will find one (sorry!). Prop and Set Design are fairly niche industries. That said, designing a top hat should not be too hard. I would start with a tin can. One of the large ones that fruit often comes in (the catering pack size). Use some stiff card arround that, to get rid of the ridges in the can, and attach a brim (again, use cardboard). If you want to give it a fabric look, get some spray adhesive and some felt.
A can is more than strong enough for someone to stand on - and it's so they can wear it. I would make sure the inside was felt lined as well, so as to avoid injuring the dancer.