you could actually go to the local river mouths and catch various species of brackish puffers, chelonodon patoca is very common, and some takifugu sp., just have to acclimate them to your tank, and keep the ph high, they should do just fine. i use to catch a few different species of them myself, much more rewarding! use a smalll piece of shrimp on a hook, and usually you'll have some following.
wes