Number of Harps in the orchestra.
David Daniels Orchestral Music 4th edition and its internet version – Orchestral Music Online <http://www.orchestralmusic.com/subscribe/index.shtml>
lists the instrumentation for standard repertoire. They have these listings for the number of Harps requested or written for by the composers:
1 harp: 2115 standard works.
2 harps: 424 standard works.
3 harps: 16 works (3 of those have 1 real part).
4 harps: 4 works [1 with 4 real parts, 2 with a doubling of 2 real parts, 1 with a doubling of 1 real part.]
6 harps: 4 works [ 1 with 1 real part, 3 with a doubling of 2 real parts.]
12 harps: 1 work with 12 harps doubling 1 real part – Berlioz: Te Deum, op.22: Marche pour la présentation des drapeaux (March for the Presentation of the Colors)