You cannot purchase music in the original Animal Crossing (GameCube). There is no in-game shop for songs.
Dynamic hourly tracks play automatically. Iconic, memorable, non-interactive.
Unlike later entries (Wild World town tune, New Leaf custom designs, New Horizons music player), GCN Animal Crossing has no custom music import. No SD card slot, no microphone recording (unlike DS/Wii sequels).
K.K. Ballad, K.K. Blues, K.K. Bossa, K.K. Calypso, K.K. Casbah, K.K. Chorale, K.K. Condor, K.K. Country, K.K. Cruisin', K.K. Dirge, K.K. Dixie, K.K. Étude, K.K. Faire, K.K. Folk, K.K. Gumbo, K.K. House, K.K. Jazz, K.K. Lament, K.K. Love Song, K.K. Lullaby, K.K. Mariachi, K.K. Marathon, K.K. March, K.K. Metal, K.K. Moody, K.K. Parade, K.K. Ragtime, K.K. Rally, K.K. Reggae, K.K. Rock, K.K. Rockabilly, K.K. Safari, K.K. Salsa, K.K. Samba, K.K. Slider, K.K. Soul, K.K. Stew, K.K. Stroll, K.K. Swing, K.K. Synth, K.K. Tango, K.K. Technopop, K.K. Waltz, K.K. Western, Forest Life, My Place, Only Me, Pondering, Steep Hill, Surfin' K.K., The K. Funk, To the Edge, Two Days Ago, K.K. Island, K.K. Song.
Visit K.K. every Saturday. Build your collection. That's the music system.