I guess I am not really sure if you would consider the IV part natural... but I have recently been coming accross this one.
Intravenous Calcium EAP (or AEP as its called in hannover, germany).
It appears to have originally had good results, but appears to have fadded into the ether. It was even supposedly recommended by Dr Atkins in his book.
Has anyone personally tried it? I did a search for it on iHerb, and found a product with it in it (calcium athanolamine phosphate)