Unless you can find a used one somewhere to scavenge parts off of the best bet is going to be a replacement. I don't know if anyone other than Zip Dee is still making the curved arm awnings or not.
Call Out-of-Doors Mart
in Colfax, NC. You want the parts dept and ask for Ben. He will be able to tell you if any repair parts are available or not.
For future reference if there is going to be a heavy rain the best bet is pull the awning in, for lighter rain you should tip one end several inches lower than the other so it will drain quickly. You aren't the first one to learn this the hard way and I am sure you won't be the last.