Since you don't have a backup of the old site, you will have to re-post all the episodes just like you did before.
You can backdate the posts to the original release date to keep everything in the correct order ( I suggest you start with the newest episodes and work backward). Since you are on the same domain name, you should be able to use the same feed address as you did before.
There isn't really an automatic way to do this. Do it just like you did it the first time.
-Mike