Barb used eBay mostly to fill in the missing pieces of this
collection. That was much easier then because eBay was
new and prices were far more reasonable. That said, eBay
is probably the best source for back issues.
For current and future years, contact Danbury Mint.
There are other after-market sites but Barb had little-to-no
luck using them. Sometimes you can also find these
ornaments at estate sales and yard/garage sales but often
condition is compromised.