It is not usually necessary to create a new script of a new challenge. The scripts are configuration. You can add an configuration for a new challenge that the existing script uses.
Post a request in the forum as noted in the other post http://project-gc.com/forum/list?8
You need permission to tag a checker and to write a script.
Download source worked for me when i tested it
I might requires that you are allowed to tag checkers or to write scripts.
A test with another account shows that it is likly the case. But the "View source..." button worked on that account to and that shows the same code as the one you can download.