The Economist took a look at the shortage in cadavers:

• Demand for cadavers has grown. They are used for medical training, organ transplants, public display, disaster dog training and car safety tests.
• Yet supply has fallen. Improved means of communication mean there are fewer unclaimed bodies.
• In countries such as China and the Middle East bodies are treated with respect and so aren’t as commonly donated.
• For the bodies to be useful they have to meet certain standards. They must be young and relatively healthy. Such dead bodies aren’t easily available (many would say that such living bodies are rare too).
• While paying for dead bodies is illegal some medical schools get around this by paying for elaborate funerals.

Read more about alternatives to cadavers, and other ways that people have started paying for bodies over here.

Source: The Economist