You may choose to create or modify your own Open Educational Resources if you do not find resources available that suit your needs.
Creating an OER is similar to authoring any other document, except that you are assigning that content an open license which usually allows for its free use and re-purposing by others.
Things to consider:
Modifying an existing OER is a a simpler way of adopting content to suit your needs than creating a new OER. Before modifying an OER, check that the Creative Commons license does not contain a "no derivatives" clause. If it does, you do not have permission to modify the work. Search for formats that are conducive to modification, such as .docx and .rtf. Once you've downloaded and modified the OER, you can upload it to many of the sites listed in the "Sites for Creating and Hosting OER" section.