[cj57]

If you google your question, there's some interesting things that pop up with several having less that 50 examples made.
This was the one with the lowest number made that I could quickly find.
Marlin Model 1893 Lever Action Rifle; Serial No. 130842; Per Included Factory Letter: Musket; 32/40 Caliber; 30” Barrel; Shipped December 14, 1895; One of 22 Made
View attachment 965969
Pretty cool stuff!

There are few one of kinds in those old models, I have a 1893 musket in 25-36, just a few, I have a 1893 in 38-55 with 27" barrel, I think the only one and a model 1895, 40-65, with 29" barrel, also may be the only one. I've seen some other odd balls in all other models from the 1881 up to the 1895

 

[cj57]

Just from personal experience, the rarest Model of which I have zero in my collection, is the Model 1888. In all my years of looking, I have never held one and only saw one up for auction and it went for about 2k over my budget. About 4800 made, over 140 years ago I can only imaging how many are left. It was quickly replaced with the Model 1889 of which I only have one. That and the 1891 are the only two I have no examples of, and the Ballards but they are less rare, just more expensive.

Yes, those 88s are hard to come by, as well as side loader 91s. Any 88 with any non-standard options, Rare!