Caught out by a Camera

I bought one of these at the weekend from a charity shop. A Kodamatic instant camera. But when I went to a camera shop to buy film for it they told me it wasn’t made anymore. Kodak stopped making it in the 80s. I looked it up on wikipedia when I got back and the reason they don’t make it any more is that Polaroid brought a lawsuit out against Kodak, and won, meaning Kodak was no longer allowed to make instant cameras. I was pretty disappointed to be honest, but was unsure what to do next. I felt it wasn’t really right to take it back to the charity shop and demand my money back…what is the correct etiquette for charity shop returns? Can you do it?…would it make me a very unethical, uncharitable person, or should I use my consumer right to get a refund? Would that undermine the very purpose of charity shops?