Scores can be found in the library's collection.
Use Primo Pathfinder to locate scores in the library's collection.
The results are videos and scores.
Narrow the results to scores by selecting Scores under the "Tweak my results".
Select APPLY FILTERS at the bottom.
This will give you a list of different piano scores by Rachmaninoff.
Piano works that are in the public domain are often accessible online. Here are a few examples.
IMSLP - Petrucci Music Library
Library of Congress - Collections of Notated Music
Sheet Music International - Free Public Domain Sheet Music
The library has books and videos on piano makers and piano construction.