Steve's right, Joplin has little to offer. I just moved from there (to Bentonville) actually, and am finally getting back online but still not really settled (still lots of boxes).
There is a Pet Warehouse on W. 7th that is poor. Last time I was there, they had an adult Niger Trigger in about a 25g tank. On rare occassion do they have corals, which is probably good.
ClawPaws is in Webb City and Pittsburg. It's okay with fish, and they're willing to order things for you. Coral selection is usually thin.
PetsMart is there but does not carry SW.
I always made a trip to Rogers when I could get the chance, about once a month, and now I'm much closer.
I made a few trips to Tulsa. Aquarium Oddballs was nice and the owner was helpful. I got a Clown Fairy Wrasse that was awesome. I had him for about a year but then he found a way to jump out.
I visited all the other stores, and some were okay and some not so much.
KC and STL have a couple of nice ones, but that's stretching the mileage.
I just still have to name ET in Rogers as the favorite.