Even if you happen to find, they will require you to pay before you advertise. I have once been in a situation where I was looking for a forum to do some promotion and the forum I happened to come across was a local forum and the mods said before you will advertise on the forum you will have to pay first and after your payment is confirmed you will be able to advertise as much as you want for a limited time.

Although this bitcointalk.org forum seems it’s free (except the space under first post on every page), anyone is free to advertise through signature space and personal test whatever here, but the way you said it, it seems you don’t want to post in this forum.