hi there -
how about take one of your just made post cards, and make a contact print with IT onto another piece of photo paper. you can get the paper wet to make a good contact emulsion to emulsion ..
you will now have a "negative print" find out your exposure ( might be the same as it was to get the negative ) and have fun making postives.
i've done this method when i was given a print and other people wanted copies of it, and i didn't have a negative, the person who made the actual print gave me her blessing to make copies since she was a few states away and i didn't really have any other options ( didn't want to make a copy negative).
--- paper negative/ internegatives work well