Some of those rare lens, appear maybe once in a very long time.
For example, Fujinon A 1200mm. I have seen two copies. One in midwest photo about 15 years ago, the other at my friend's collection.
Fujinon SW 300mm. Once I thought this was one of those lens that only exists in the catalog, until I saw one for sale (or link for sale) in one of the posts here.

But some lens I have only seen them in the catalogs.
Hypergon 200mm. I have never seen a photo of such a lens.

What are other mysterious lens maybe only exists in catalogs?