Casting for voices is rather rare. But production companies are always on the lookout for the right voice. Make an account on Soundcloud first, upload your self made recordings (you can do this with a laptop or smartphone in a quiet environment) en send in a link to a production company.
If you first want to discover your voice and fine-tune your timbre, take a look at this overview of voice coaches.
Are there any Belgium-based casting agencies you believe are missing from this page?