Hi doshspy,
You may have read this already but just in case you haven’t … post #2 here has links to most of the better forum posts or threads that are about mattresses and children and include some good sources for children’s mattresses as well.
I don’t keep a list of specific mattresses or designs that any store carries (it would be an impossible job with all the changes that happen on a regular basis throughout the country) but innerspring / natural fiber mattresses are not so common in the industry. There is a list of some of the manufacturers that make innerspring/natural fiber mattresses in post #4 here and you could call them or check if they have a retail store locator on their site to see if there are any retailers that carry them in your area. Most if not all of these would be much more costly than the Pure Echo though. I did a quick scan of the Washington DC list and Mattress Traditions carries Hypnos and Urban Mattress carries VI Springs but both of these are Ultra Premium brands in much higher budget ranges.
Phoenix