There's a lot of places.
Miracles
Deep Sea Aquatics
Reef Savvy
Glass Cages (the low end of custom tank builders)
Just to name a few. I know there is more... one on the west coast that's on the tip of my tongue but i cant remember. Might want to do a search on Reef Central. I know the subject has come up a lot. The main problem tends to be long lead times of a few months or more. From what I've seen. Mine was ordered through a local shop who used DSA and it took over two months if I remember correctly. You might want to give your local shops a call, see who they use and maybe get some quotes from them. It's nice to have a local place to lean on if anything goes wrong. Also, most tank manufactures require you to purchase their stand to have a warranty on the tank. With mine i just got a plain support stand from them since I knew I was going to cover it later with custom cabinetry.