The eureka beaker is a beaker to find out the density of irregular shaped objects. Archimedes invented it when he stepped into his bath and saw that the water level rose. He shouted "Eureka!" which means "i have found it!".
You can order them from any number of suppliers... a couple you might want to look at are Fisher Scientific and Sargent-Welch. If you have a friend who works in a laboratory (or if your parents do)...