before I begin, you should know that I am not as experienced as some other members, so you may want to double check with another person before taking any serious action.
Best thing for fin rot when you have no meds at at your disposal is CLEAN WATER. Clean, clean CLEAN water is necessary. Make sure it's dechlorinated. Some people say a bit of aquarium salt is also good, and I do add that to my tanks, but you may want to double check with someone else for your particualr case.
If you can get a product called API Stress Coat, it's good for the fish and it removes the chlorine from the water as well. A lot of people on this site have recommended it to me, and in my experience, it works wonders. I won't use any other water conditioner except this one!
If you can tell me what country you're in, I might be able to help you get the medications you need. I know in Canada, certin products are very hard to come by, but I have a link or two that might be of some help.
Let me know, and good luck!