There is an Aroma Lady Hannah that has a lv. 16 Combee West of Hearthome City.
However, to catch one yourself look for a tree where you can smear honey on it (i.e. Floaroma meadow), and wait an hour or so. Then check the tree, you may find a Combee.
Pokemon to be found on trees: Aipom, Burmy, Combee, Wurmple, Cascoon, Silcoon, Heracross, Munchlax, Cherubi.