Thank you for getting back to me. It would not be legal for me to give you specific information, such as dosing instructions, in an online forum. I can tell you some general facts about birds and antibiotics. The most effective broad spectrum antibiotics are often unsafe to use in birds. Birds are too sensitive to them. Baytril is one antibiotic that is often used. Most of the antibiotics sold in pet stores are old ones that are no longer effective because bacteria have become resistant to them.

As you've already found out, cat bite wounds are very prone to infection. It can help to immediately clean the wound with a povo-iodine solution (such as Betadine). These are usually available in pharmacies, drugstores, etc. You can use povo-iodine twice a day. I suspect that some of the birds you find already have a systemic infection when you rescue them, and in that case they will need a systemic antibiotic given by injection or mouth.

An option for you might be to contact a wildlife rehabilitation center. Such centers often have veterinarians who work with them and have access to the needed antibiotics. They may be willing to take the birds. If this center isn't near, call or email them to find out if they know of another.