Can anyone recommend a foot deodorant for babies (if it exists, safe to use)?

I have never encountered any foot deodorant for babies and I don't think it is really necessary. The concept of deodorant is to mask the smell and most of the time, they contain harmful chemicals which are detrimental to the health of the baby. I would suggest washing the baby's feet and keeping it dry. If the baby has not started to walk yet, let him/ her wear cotton socks instead of "baby shoes". These baby shoes are solely for aesthetic reasons and most of the time, they trap in heat and moisture, which encourages bacteria proliferation, thus the smell. If your baby has started walking, invest in good shoes for baby that is ergonomic as well as breathable. Hope this helps :-)