I have sent some emails over a month ago, and no replies
Not sure what else to tell you. TL is notorious for doing everything in house. You can't even volunteer to work this event unless you are a part of an organization and have a certain size group of people. They really do lock everything down and control every aspect. There is no news on the internet as to how they choose their vendors for TomorrowLand either.
That's true, ID&T does everything with the people they allready have. So no volunteers will be allowed on the festival, mainly because ID&T don't want people to take advantage of the fact they enter the festival for free (and as a result don't work that hard).
But as Kai has said, if you have a group, you can always apply on helping on TMW (most of the time this will be at the Dreamville camp site). This was done in Belgium many times.