Type into google "(insert state here) aquarium club"
Or look on Facebook for fish groups and you may be able to find some locals that way or be recommended to a local group.
Fish magazines like Tropical Fish Hobbyist have aquarium clubs listed in them as well, and you can also check with members here to ask if they can look in a magazine for your state's clubs if you can't find/buy the magazine yourself.
I personally had a lot of luck with Facebook. I found 2 clubs in my general area and have been told of 3-4 others and have met quite a few local breeders and enthusiasts this way. I'll be attending my first fish auction next month because of it.
Hopefully this helps