These new horn sounds now exist in your game. Use fastman92 limit adjuster, GTAAudioMetadataTool (https://github.com/ook3D/GTAAudioMetadataTool_V2) or RAGEAT to add them to your vehicles.

ASTEROPE_HORN
BENSON_MULTI_HORN
BRAWLER_HORN
BROKEN_HORN_MARBELLE
BROKEN_HORN_VOODOO
DESIGNERS_VAN_HORN
EMPERORC2_HORN
FELTZER2_HORN
FELTZER3_HORN
FENRIS_HORN_MT
JACKAL_HORN
JOURNEY_HORN
KURUMA_HORN
MASSACRO_HORN
NEMESIS_HORN
NINEF_HORN
OSIRIS_HORN
RAPTOR_HORN
REBEL2_HORN
RIDGE_HORN
RUFFIAN_HORN
SENTINELXS_HORN
SERRANO_HORN
SURFER_HORN
T20_HORN
THRUST_HORN
VOLTIC_HORN
ZENTORNO_HORN