The Music section of the HBLL collests scores suitable for instrumental musical numbers. Find them by searching "Mormon Music Collection" in a general keyword search.
Search for the item by call number, with compositions by LDS composers designated by a .8 after the call number (so, for example: M 242.8, or M 221.8).
M 221.8 = violin and piano
M 226.8 = viola and piano
M 233.8 = cello and piano
M 242.8 = flute and piano
M 287.8 = string duets
M 289.8 = wind duets
Ask staff for more help with particular instruments.