- WorldCat Discovery
Microform is a subformat of Book. If you do just a regular search with no format filter you will get microform titles in the results. You can then use the Microform option under Book on the left hand side facet display to cut the list down to just microform.
You can also use the material type index (mt:) to limit to just microform materials using: mt: mic
There is more about the material type index.