Hi Robp8888,
You may have seen this already but some of the better options I’m aware of in the Cleveland area are listed in post #2 here and it may be worth making a few calls to see if any of them carry a foundation that would be suitable for an all latex mattress.
It’s not uncommon at all that retail stores don’t have a great deal of knowledge about latex mattresses or the type of foundations that are most suitable for an all latex mattress but if you can’t find a good quality slatted foundation locally then the foundation post here has some good sources where they are available and also has some DIY foundation designs that were shared by some of the forum members here (although you may have already seen this as well).
Phoenix