Setting up the wiki should be easy, just create the page.
However I don’t think you should do that until you have a working mailing list or forum that is able to come up with good consensus decisions on what should be on the page.
I’m afraid I don’t know who to contact to set up a mailing list or forum, but would suggest that you should be starting with a mailing list, rather than a forum.
Are you really sure that there are enough long term residents of Vanuatu, or natives, who are contributing to the map to create a successful community? Even some European countries (which are generally the most extensively mapped) seem to have forums that don’t have critical mass of users.
I would probably start by private mailing active mappers in Vanuatu, particularly ones who don’t look like holiday visitors, to see whether they would be interested.