Book-straps were very commonly used by students in the late 19th/early 20th century to carry a relatively small number of books to and from school.
I've consulted several 19th and early 20th century French-English dictionaries, and performed very exhaustive searches on eBay.fr and other antiques-related French websites, but can't find the exact term I'm looking for.
'Un porte-livre' (a term that is still in use in modern French, from what I gather) seems to be a stationary stand for holding a book on a table, etc., and the term (based on my research) meant the same thing in the 19th century. 'Un etui de livre' also still seems to be in use in modern French, but (at least nowadays) seems to mean a more solid/substantial (i.e., not composed of straps, with large gaps between them) carrier for a book (or even for a small electronic device, etc.). The latter term was used in the 19th century, but I'm not certain what specific meaning it had then.
'Un sangle de livre(s)' (or 'des sangles de livre(s)') does not seem to have been in use the 19th or even early 20th century, though I've found this term being used in modern French to refer to an antique book-strap, or at least a modern reproduction of one.
Any suggestions of possible words (or compounds) that anyone has to offer would be very much appreciated!