I have found out I can use nmbs.be to search for buses of both delijn.be and infotec.be. The 'problem' is that it also includes trains no matter what you choose in the advanced options.
Is there any search engine that allows searching for just buses?
The reason that I am asking is that I am trying to figure out the cheapest route between two points and as both TEC and De Lijn have relatively cheap long distance/day passes (less than the sum of a bus ticket + train ticket + bus ticket) I am trying to find a route between Leuven and Charleroi Airport by bus. Additionally Google Maps only includes buses from De Lijn and I have been unable to find any other service.