My 6 year old son is a bug fanatic. So we've had our share of critters. Mantids are awesome.
We've found it best to keep one to a container otherwise one may eat the other. Just feed them crickets. It's so cool to watch them feed.
You shouldn't need to buy them, just look around the garden during summer. There should be some beuties out there about now. Nice big ones.
Mellissa