"It's near the Bibliothèque Nationale and the Sorbonne."

Bibliothèque Nationale
Creative Commons Attribution Share AlikeBibliothèque Nationale - Credit: Sailko
At the time of the novel's events, the Bibliothèque nationale de France was located on rue de Richelieu in the 2nd arrondissement, on the Right Bank of Paris. (The library has since expanded and new buildings were constructed, but the Richelieu site is still in use.)

La Sorbonne
Creative Commons Attribution Share AlikeLa Sorbonne - Credit: Maksim
The Sorbonne, Université de Paris, is in the Latin Quarter, in the 5th arrondissement, on the Left Bank.

Larry lives in the Latin Quarter. Bear in mind that Paris is eminently walkable.