If you would like to browse the stacks in the Library or the ROC for scores, try the following call number ranges for harp, guitar, and ensembles with one or more of either instrument:
Harp
M115-119 Solo
M273-274 With piano
M1036 Concertos with orchestra
M1036.5 Cadenzas
M1037 Concertos with piano
Guitar
M125-129 Solo
M276-277 With piano
M1037.4.G8 Concertos with orchestra
Ensembles
M292-293 Two plucked instruments
M294-295 One string and one plucked instrument
M296-297 One wind and one plucked instrument
M325-M329 Two plucked instruments and piano
M365 - M369 Plucked instruments trios
M447 - M486 Quartets which may include one or more plucked instruments
M467 - M469 Plucked instrument quartets
For Quintets, Sextets, Septets, Octets, and Nonets use the same formula as Quartets and Trios (i.e. Plucked instrument octets would be M865-869).