I want to publish here an ad banner. Who I can contact?
As said, ad banner handled by the forum itself is no longer an option.
If you are okay with having a number of people paid to wear your ad in their signature area, hence visible on all their posts (new and old), you can do signature campaign, also as mentioned already (just look at the bottom of my post, you'll see that I am wearing an ad myself).
Keep in mind though that it's
advised to have an announcement (ANN) thread, so people can contact, ask various questions, ... (you can maintain it or hire somebody to maintain it).
Also keep in mind that when your signature campaign ends, people will start wearing others' ad and yours will probably no longer be visible (unless somebody wearing your ad becomes inactive, but that's rare).
The signature campaign can be handled by you (but then you will probably have to escrow some funds because you are too new, hence there can be trust issues), or you can hire somebody (unsurprisingly, I recommend the campaign manager that's also handling the campaign I'm in).