Using the library catalogue, do an Advanced Search and then limit to material type MUSICAL SCORES:
NMA Online is an impressive ongoing project to make the complete works of Wolfgang Amadeus Mozart (1756-1791) freely available online. Currently, it provides access to 126 volumes and over 26,000 pages of music, as well as the critical reports and eventually critical editions of letters, documents and libretti.
by Akbar Simons
Searchable and browsable by Köchel number, keyword, genre, key, and more. Interface available in German, English, and Japanese.
When you have found the desired volume: