Yeah pulling the peizo out of the little radio shack buzzers is a pain. There are plenty of places to buy piezo transducers. Aside from the website you mentioned there is also mouser.com, digikey.com, jameco.com, Newark.com. There is also users on ebay that sell them. I personally have used mouser.com, and newark.com to order all types of electronics parts. So I can vouch for how good those companies are with online orders.