Our club began when an advert appeared in the local paper asking people interested in forming a fish club to ring the phone number given, so we did. They then arranged for all to meet one Sunday afternoon at their house and it went from there.
These days you can also put posters up in vets, libraries, any community notice boards you have, malls, supermarkets, schools etc.
Another thing, if you have a free community paper, ask them to do an article about you wanting to see if there was enough interest in forming a club. Alternatively, just do the poster thing (and the advert in the paper if you can afford it), wait until you have enough interested to form a club then go to the paper and ask them to do an article on your newly formed club.
I am happy to supply posters for you if you tell me the details you want on them. I can do them in colour for you too so they will stand out.
If there is enough interest and the club gets off the ground you may then consider whether you want to join the FNZAS. This gives your members access to the free Aquarium World magazine and a Year Book listing, among other things, all the other affiliated clubs in the country and their members' details. It also lists all retailers offering discount to FNZAS members.