I’m still collecting 20mm WW1 tank kits with no real purpose in mind other than I like it, though I often consider some sort of Plan 1919, the ideas were there for the genesis of modern mechanized warfare but (fortunately) the war ended before they had to be implemented.
These two are from Early War Minitures: http://earlywarminiatures.com/
We have a Mark V female which made its debut at the Battle of Hamel and a Mark IX supply/ personnel carrier tank, a few were finished by the time of the armistice but did not any service.
The last Mark IX can be found in the Bovington Tank Museum.
I did find this short video of a Mark IX being used for amphibious trials post- armistice.