I had to think of 3D printing immediately when you mentioned the human heart model: such things used to be incredibly expensive, but today any makerspace would be able to produce a respectable replica for pocket change or might even donate it for a mere mention. 3D data is often available under free CC license, e.g. https://www.printables.com/model/5612-anatomic-heart-multi-m...

Entry into this tech has become pretty cheap (a few hundred bucks for an entry level printer) and much more accessible in recent years. Maybe a volunteer/intern could help set you up.

Edit: NVM, I only just realised that was probably a _walk-in sized_ heart you're talking about. That's probably not gonna get cheap to produce anytime soon...