In a place as large as Auckland I don't think you need to worry about 'stealing' members from other clubs. Actually we have a number of people who belong to more than one club anyway. My own club also has Auckland members
If you have at least 3 of you keen to give it a go then start from there. If you wait for people to register interest first it might be a long wait. A lot of people don't know about this site (sad but true) so you are only getting a small section from here. I am happy to make up some advertising posters for you (and print them in colour) to put up on local noticeboards, supermarkets, libraries, vets, petshops etc. Decide on a time and place then advertise you are holding a meeting for all people interested in joining a local fish club and see how many turn up.