Here are a few places that sell NA native fish. I've only personally dealt with the first link, and will give them the highest marks for product and service.@catfishnut - There are certainly a lot of different reasons to keep native fish. While I do enjoy my goldfish and koi, to me the pond felt very unnatural just having the one type of fish in it, and you can't generally go to your local fish store and pick up much that would survive a full-blown Winter. I'm crossing my fingers that the weather loaches do well and are much more visible this coming year. And now that the pond is really established, I'm going to try and really get stocked up on more rosy-red minnows. If I can just find a source for something like those greenside darters, and pick up a batch of leopard frog tadpoles, I think I'll have a good variety to watch in the pond.
@mmathis - Mostly its a matter of research. I read up first on what temperatures a species can survive, and then on what they like to eat. Finally you want to check out how their native waters correspond with your pond. For instance, part of my interest in the darters is that they are bottom-dwellers from rivers. They would likely be found in areas on my pond that the goldfish are not interested in, and their movement in those areas will help stir up any decaying matter that might try to settle in. The same for the rosy-reds... they like hiding under the larger rocks and clean out those areas. Without the rosies, I would have a mess of decaying plants in my rocks around the edges. This is the thoughts behind my desire for a variety of fish -- different species will occupy different regions of the pond, eating different types of foods, and hopefully helping to establish an even more natural overall balance.
www.aquaculturestore.com
http://www.btdarters.com/