You need to check out your vbulletin stylesheet and check the header or navbar templates whereever those links are and add one for the forum.
I can't say where this is going to be as this is not a classifieds issue. We are talking about a custom
vb theme and these links reside in the templates for that theme. You need to poke around that theme. I would think it would be one of those two templates as we only call the header navbar and footer templates over classifieds