Music scores from the UvA collection can be found in the UvA catalogue thus:
If you wish to search by composer, use search key Author.
If you are looking for music for a particular instrument, use the search key Words from title. Note language variations:
piano OR klavier.
If you are looking for a specific combination of instruments, use Words from title, and be aware of language variations, search e.g.
“string quartet?” OR “quatuor? a cordes” OR streichquartet?
The question mark is added to search both for string quartet and string quartets, etc.