Yeah, I've used a couple of times dollies called Roll-or-Karis. True to their name, they do indeed roll, and if you have some people you hate, you could probably convince them to "carry" a piano or organ as well.
They're kind of standard equipment for people who want to move Hammond organs (I think those are generally about 400 imperial pounds, IIRC), and can easily be rented most places, I'd think.
No idea if those particular dollies are what's needed for a heavier piano, or how to adapt them for getting under the legs, but if not them, something similar is surely available.
Up to and including the more traditional "truss" like support with wheels at least some stage pianos seem to live permanently on.