Maybe not in the same quantity but from personal experience Rosario, Mendoza and Córdoba are decent sized cities with a book-reading student population.

I visited several nice bookstores across the river in Montevideo and Punta del Este too! :)

I haven't been to too many Argentinian cities outside of Buenos Aires, but Mar del Plata also has some nice bookstores in the center. I would guess at least La Plata, Rosario, Córdoba probably do too.

I was about to say the same: Argentina isn't a "capital" of something, it's a country.