Go the The Roost cafe (basement of your museum) on Saturday nights between 8:00 p.m. and 12:00 midnight and talk to K.K. Slider. when he asks you if you are there for a song, say "No thanks" and sit down until the song is finished. He will then give it to you for your radio and ask if you have a request. Below are all the songs you can request, which are case sensitive.
Agent K.K Aloha K.K. Cafe K.K. Comrade K.K. DJ K.K. Forest Life Go K.K. Rider I Love You Imperial K.K. K.K. Aria 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. D & B K.K. Dirge K.K. Dixie K.K. Etude K.K. Faire K.K. Folk K.K. Fusion K.K. Gumbo K.K. Jazz K.K. Lament K.K. Love Song K.K. Lullaby K.K. Mambo K.K. Marathon K.K. March K.K. Metal 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. Ska K.K. Song K.K. Soul K.K. Steppe K.K. Swing K.K. Tango K.K. Technopop K.K. Waltz K.K. Western King K.K. Lucky K.K. Marine Song 2001 Mountain Song Mr. K.K. My Place Neapolitan Only Me Pondering Rockin' K.K. Senor K.K. Soulful K.K. Steep Hill Surfin' K.K. The K. Funk To the Edge Two Days Ago
Notes: The "K.K. Song" is actually music from Mario Paint. The "Forest Life" song is the theme from the original Animal Crossing on the Gamecube.