I don't know why you're getting that message. Are you outside of the U.S.?
Not trying to be nosy but why do you want the source codes? Are you trying to update a Kindle or are you just curious. There are a couple of stickies at the top of this forum. One with source code links and the other with change logs. If that's not what you need maybe I or someone else can direct to what you're looking for.