There are many antique shops in Warsaw, but not many bookshops with used books, and not all can be recommended. Most don’t have web pages to search for books or objects you want to buy. They’re mostly located in the city centre, specifically around Krakowskie Przedmieście, in the university surroundings, and next to Trakt Królewski passing.
Antykwariat Warszawa doesn’t only have books in Polish – it also has a wide selection of art & culture books, including, for example, photography albums and some books in English (check here). Also, there are some old pins and posters (check here), postcards (check here), and advertisement materials (check here) that could be a great gift from Poland.
Located just on the other side of the street from Bar Wieczorny, make sure to check that article as well, and this makes it a perfect programme for an afternoon-evening cultural activity in the district of Mokotów.