u have to use the honey on the trees to lure them it takes time wait around six hours and check also there r some trees that have higher chances of rare pokemon so the best way to get is to go and smother aas many trees as possible in the smallest period of time and the game will reset the clock if u make time fastforward with the ds
so goodluck srry about the very very very very late reply
I'm not trying to sound mean but you do know what this person is playing Heartgold/SoulSilver... You don't smother the trees with honey anymore...
Anyways try the trees around kurt's house thats where I found Aipom on my HG. Headbutt those for a while and you might not only find a Aipom but a heracross too.