There is a product that is topically applied that a lot of people on this thread use that is anti-fungal. Some feel that it is not "natural" (that's the disclaimer) but it does work very quickly and has antifungal and antibacterial properties.
I don't think anyone has found it local, but have to order it. It's called NuStock.
http://www.amazon.com/Durvet-001-0530-Nu-Stock-Ointment-12-Ounce/dp/B000HHSIYQ
It has a very strong smell is is mainly sulphur and pine tar. Also has
mineral oil which will leach oil soluble vitamins out of the system (Vitamin A/D/E/K are oil soluble...they will bind to mineral oil and taken out of the system with it) so it should be used carefully in my opinion. Likely the strong smell will encourage folks to use it judiciously

(I always wonder why these medications use mineral oil as the oil carrier...there are plenty of other choices that could work....)
The stuff really works topically and you don't have to use it long.... There is nothing I can find that states that it is approved for use in poultry. I, personally, recommend moderation if you decide to use it. I do have it in my first aid kit.
For the system itself, using a probiotic that is designed for poultry will help restore the system. The ONLY avian probiotic that I recommend is
AVI-Culture 2. It is grown on a non-gmo substrate.
I spoke with every major producer of probiotics for Avian use and
this is the only one that uses a non-gmo substrate. I spoke with the owner of AVI-Culture at length and am very happy with the product.
Their website leaves a lot to be desired, but the product is good. Only need a small container as it lasts a long time.
http://www.nationalbirddesigns.com/shop.html
It also makes a GREAT "jump-starter" culture for those of you that are using lacto-fermented feed,