Dear Jari,
there should be at least one : L'Aeroteca Miguel Creus.
In 2002 it was in in calle Congost, 11 that is in the Northern part of the city, going towards the Guell Park (if I'm not wrong). It was a very nice specialized bookshop (at least for an Italian standard) full of very interesting (and never seen before or after) books in Spanish language -of course also a very rich selection of English titles. Searching in the net I've found its Internet site
http://www.aeroteca.com and now the address seems different: calle Montseney, 22. Go for sure because its a place worth a visit.
Ludovico