Where can I get band merchandise?

I like these bands/artists All american rejects, Anberlin, Armor for sleep, Avril lavigne, Boys like girls, Billy talent, Blink 182, Daft punk, Dashboard confessional, Decyfer down, Disturbed, Enter shikari, Funeral for a friend, Fightstar, Go audio, Gym cl heroes, Hawthorne heights, Hoobastank, The klaxons, The kooks, Linkin park, Lostprophets, Madina lake, Panic at the disco, Paramore, The pigeon detectives, Plain white ts, Scouting for girls, Snow patrol, Tatu, Three days grace, Tokio hotel, Tokyo police club, You me at six, 30 seconds to mars, +44