To search the microform collections at UCI go into Library Search and click on "Advanced Search". Try some general search terms in the "Any Field" box. (e.g., Medieval and England). Then scroll down and in the "Microform" box, select "All Microforms". (Do not select "Any"). Then try to find the guide to the collection (in the library or online), as the guide is extremely useful for locating specific documents.
Microform sets and government fiche are located on the second floor in the Grand Reading Room of the Science Library.