The Buy Section rules changed on June 3rd, and the mod also mentioned the following on a question:
So for older members that did already have a WTB thread (which complied to all other rules - i.e. prices mentioned and no trading allowed), could still update and/or bump it. Creating a new WTB thread isn’t allowed below 50 posts however.
Might sound a bit unfair to new users, but this forum is one and foremost to share collections and have discussions. The Buy section is just a nice bonus. Just make a welcome post in the welcome thread to introduce yourself; perhaps share your collection in the Collections Additions section; and just engage in some of the discussions in general, and you will have reached 50 posts before you know it. 
Greetz,
Quuador