Second hand English books
Various churches do 2nd hand book sales, so does the British and Commonwealth Women's Club and the British School of Brussels.
These tend to happen towards June time, just before summer holidays.
Pele Mele in central Bxls is worth a try.
And I have literally hundreds of books in English which I am always keen to exchange if you have similar genres - mysteries, thrillers, suspense novels and similar.
Email to kasseistamperATyahooDOTcoDOTuk if you are interested.
Check out this excellent second hand English book shop in Ixelles, near Pl. Fernand Coq : Tulibris at
Rue de la Tulipe, 25
If you're looking for specific books, it's worth looking on Amazon France or UK for second-hand. Lots of sellers there send books to Belgium, and even with the postage, it's a pretty cheap way of getting books in very good condition.