The problems in this set are from a variety of sources. Some are from the Library while some are stashed in local directories.
In general, to be able to view the source code in WeBWorK requires that you be an instructor of the course. Since you are likely logging in as guest then you can see only what a student might see which should not include the source of course.
If there is a particular problem which you are interested in, please send me an email and I will be glad to point you toward the source.