The only commercial source I know of is actually in FL. They ain't cheap though! http://www.aquaculturestore.com/Fresh-Water-Vertebrates/?page=4

If you have a predator free pond, just 10-12 will do. If you give them the chance to spawn a time or two before predators are introduced. Even if you just give them a chance to get big enough to not get eaten, you can then allow them to spawn and hope some of the YOY survive. Or you can buy some of the larger adults they offer.

My LCS have done very well in a .34 acre pond. They spawn in northern VA where I am in late March, early April in the shallows. It is about the only time I ever see the adults. They come into the shallows, the males fan out areas to clear away the silt and then groups spawn in the clean areas.

The YOY are now about 1.5" long this year and rove in schools of a few dozen fish working the bottom for food. 1 year old fish are 3-4", 2 year old fish are 5-6", 3 year old fish are 6-8" and my original stockers from back in 2009 are now 7-10" in size.