I saw your post, but since I'm not part of swaps yet, I wasn't able to comment or really knew what you were talking about.
I can tell you that you can purchase postage online. You can go to
https://www.usps.com I know that there is somewhere you can purchase the postage. You most likely can sent them via email the postage I think. Check it out. I would have posted it on the thread but I'm only allowed to read not post on the swap threads.