If you want to fly taildraggers you'll have to go the Brasschaat AC, North of Antwerp, they have 3 PA-18-95
Other clubs renting PA18 are at Verviers & Spa but that's a bit far from Brussels
Grimbergen is the closest field to Brussels and has 2 clubs
VC Grimbergen : 4 C152, 1 C172 & 1 Archer
Sabena Aeroclub : 3 C152, 1 C172 & 1 Archer
Deing