companies in Brussels

Not really the way to go.

Decide what sector and job you would like. Research companies in it. Research companies with a office in Brussels, Research who in those companies is responsible for hiring and if you can connect with anyone through external events. Then see about your CV. I personally wouldn't want someone who didn't do all the work themselves. Good luck!

Agree with that. In this modern day and age, if you can't work out who does what in your sector and who to send your CV to (and it needs to be very targeted), then you're unemployable anyway.

second these answers, a very precise research and match-making before is 100% due - otherwise you are wasting your time, money and the time of the organisations / companies.

Re to your inquiry: I believe at the libraries around Schuman, you can buy an (annual?) directory with contact information & info of all Brussels EU related organisations / associations / companies. Sorry don't remember the title.