Well, you can find accessories at the florist in Floaroma Town (costs berries), also at the massage lady in veilstone city (she gives one massage to a pokemon once a day and will give you an accessory at the end), also in Amity Square in Hearthome City (must have a cute pokemon with you. It will pick up 1 item every 200 steps). And then you get accessories if you win a contest, and also from random people from time to time.
