Neko, on the way to the Café Livre, just a few doors away at no 9 rue St Martin, there's a really nice art bookshop called Mona Lisait ("Mona was reading" -- it's a pun on the Mona Lisa).
It's worth making a small purchase, just for their really cool plastic bags which have a lipsticked Gioconda adorning them.
http://www.monalisait.fr/points-de-ventes.php
I got some reproduction tapestry patterns and some art postcards there not so long ago.