It sounds like you may have traveled over the whole map without going to the Tree of Dreams. Go there and hit exit or whichever option sends you back home. You can then go back to the Island of Dreams and look again, though there is a chance you could go somewhere other than Sparkling Sea (but this can be influenced by the type of Pokemon you have).
Anyway, just return home and go back as many times as you need to, you can play on the Island of Dreams for the full hour you're online OR until you make a wish for a Pokemon to return with you. Also, if you play with every Pokemon and wait until the last five minutes to make a wish, you will see all of the Pokemon you encountered today, but only from today.