We will look on:
– eBay
– forums
And in terms of dealers/stores that sell, you may wish to try:
swisswatches-andmore.com. We used them for an old NOS Heuer Carrera crystal, and they carry a wide variety of items (movement parts, crystal, crowns, etc.). Parts come and go, so you’ll want to visit them regularly to see if what you are looking for crops up.