If you go to the Library Browser and select "National Problem Library" (which should be selected by default), then under "Subject:" select Algebra and you should see something like "There are 4999 matching WeBWorK problem files" meaning there are 4999 problems classified as Algebra. The "Chapter" and "Section" divisions further classify these problems.
To access the College of Idaho problems directly, instead of selecting the "National Problem Library", instead select "NPL Directory" which gives you a directory view. Then when you scroll down the listing you will find the College of Idaho listings and a whole lot more. In particular, you should also look at the Utah collection since they wrote a lot of algebra problems for Business Algebra, College Algebra and Intermediate Algebra courses.