Commodities you cannot buy

While reading an article about collaboration of science museums I came across a strange economical fact: You could not buy a robot dinosaur model at 1996. This fact (btw: meaning the end of one long-year museum cooperation), seems to be quite contradictory to what I know about economy, both in a mainstream and in a Marxist understanding. The authors of the article claimed that manufacturers of the dinosaurs based their business on leasing fees but this does not explain why it is not possible to buy a model---the manufacturers shouldn't care too much if they get their money in one payment or over some years. I really cannot make sense of this story, and I'd be really interested if there are other products that are commodified in this strange way.

PS During my research on this topic I found out that the Natural History Museum in London became a retailer (yes, now they also the stuff) for dino-models. Modern capitalism is really complicated...