Making homemade piezoelectric crystals, testing crystal ignitor from a barbeque lighter, extracting piezoelectric disks from gift cards, buzzers and in general, playing with piezoelectricity.
Rochelle salt crystals - Making homemade piezo crystals
Piezoelectric crystals can be made from scratch using household products found in grocery stores and maybe even your kitchen: baking soda, cream of tartar, distilled water, ...
Where to get piezoelectric crystals
You can buy piezoelectric crystals from a variety of places online, from searching for "piezoelectric" on ebay.com or your country's version of ebay, other marketplaces or commercial manufacturers and retailers.
You can also find a variety of types of piezoelectric crystals in all sorts of things that you can take apart, some of which are shown below.
You might be able to find a piezoelectric crystal in a microwave oven as well. If your microwave oven makes a beeping sound when food is ready then it may have a piezo speaker inside. If the microwave oven has a dial-type of timer that makes a bell ringing sound then it doesn't have a piezo speaker. On the second half of my page about crystal earphones I show how to get one of these from a microwave oven.
Below are some webpages where I show examples of taking piezoelectric crystals from things.
Making use of piezoelectric crystals