Hi Megan,
Hopefully you are aware that Penn State is the regional depository for maps? Be in touch with Nathan Piekielek or Heather Ross on my end as needed, see:
https://libraries.psu.edu/maps
In the meantime I had to chuckle when I read your post because I am one of four individuals on a steering committee within ALA's Map and Geospatial Information Round Table (MAGIRT) actively working on developing an online directory of map collections across the country. What we aim to do is take the last edition of Guide to U.S. Map Resources (published in 2006) and make it an interactive, map-based, quasi-fourth-edition with hopefully more content than the third edition and with the ability of map curators like yourself to manage/maintain your specific entry about your collection, i.e., to move from a static product that goes out of date fairly quickly to an active one in which hopefully the information is kept relatively up to date.
So, as you can see, if we had our Online Guide to U.S. Map Collections done it would have been a great resource for you. We are making progress though!
Sincerely,
Paige Andrew
Cartographic Resources Cataloging Librarian
Penn State University