The broken links need to be fixed for the new file locations.
The problem techniques on the WeBWorK Wiki are deprecated though. The new location for the problem techniques is https://openwebwork.github.io/pg-docs/sample-problems/techniques.html. This is the first link on the https://webwork.maa.org/wiki/Authors page.
As Alex said, for webwork 2.18, the sample problems and POD are available from the problem editor and served by the webwork2 installation.