You can get VetArk probiotics from pets at home. I have used this alongside baytril and on one occasion when a guinea pig was recovering from illness. I found it very good, and comes as a powder to mix in with water bottle. As it is a powder it has a long shelf life. My pigs loved it, but I know some pigs won't take it, so if you are going to use it, observe to make sure your pigs continue to drink. Good product to have in your store cupboard.
nb. Not sure why exactly you want it, so please take my information as general, based on my own experience. I can't advise you on illnesses. x