The Goethe-Institut offers all residents of Belgium free use of the
Onleihe [the digital library of the Goethe-Institut].. In this digital library you can borrow e-books, e-papers, audios and videos for use on your PC or mobile device.
Publications supported by the Goethe-Institut Belgium can be found here (some for direct download):
Publications
Specialised collections on Germany / in German are offered not only by many university libraries but also by numerous city libraries, e.g.
ULB library
UA library
Muntpunt library
The library of the German-speaking Protestant Congregation in Brussels is also open to anyone interested.
https://bibliothek.degb.be/
German-language media can be bought in some bookshops and press shops, e.g.
Gutenberg,
Filigranes ,
Librebook etc.