Sadly, after more than 20 years of designing, it's not practical to maintain availability for each and every design -nearly 500 in all. If the design has an entry on this website, it is available for your retailer to order.
However, for items you are not able to locate, this list of Discontinued Titles notes all of the 200+ no longer in print. This doesn't mean you cannot locate them - perhaps they are still in a shop's inventory or in a friend's stash who is willing to lend or trade. Online resources are also available for legitimate stash trading to help you locate that elusive unicorn chart.
Many, many thanks for your support over the years - I look forward to continuing for quite some time!