Any HM dealer.
Went to one, here's my thoughts.
Without a real trial it's hard to tell what is better for back support. I got the feeling that the embody gives better overall support helping you seat in the right way vs the aeron which has great lumbar support but you have to be seating perfectly (IMHO it doesn't feel much different from a regular chair).
Is there any major difference between the embody for gaming vs the regular one?
According the salesman, the chairs are overall the same, the gaming version being a bit more breathable because of copper in the fibers (and it's cheaper!).