They can add a new one when it comes to a service, but they shouldn't be too hard to track down loose.
Keep an eye on the "Watch Parts and Accessories For Sale" section of this very forum.
Alternatively, you could put out a Want to Buy (WTB) post too. They're also pretty easy to fit too.
You can also find them on Ebay easily enough, but I'm not too sure how many are legit.