There are a number of ways that city directories can be accessed.
1. Find out of your local or regional library has a geneology section and what it contains. It may contain city directories.
2. If you are in the same city as a National Archives Branch, they may have the directories you need on microfilm.
3. I think the best way is to search for "city directories" or "city directory-specific city" in a search on line at the LDS site. If they have a copy of a specific directory you are looking for on microfiche or microfilm, it can be ordered thru your local LDS family History Center.

Hope this helps.
Robin
Who has found city directories invaluable for all sorts of geneology! <grin>