Eek! Smaller is right: more like tiny!
These could be mini books in 1:12 scale or oversized tomes in 1:24 scale.
The covers can open and there are blank pages inside (see one of the extra photos above).
None of the collage sheets with covers fit these exactly, but you could buy a sheet in digital form and downsize to fit.
Set of 4 (mixed color spines as shown).190915LM 210114SC 211121new spine mini 200924new 201105SC