You can catch a Heracross by using headbutt at the small trees on various routes. You may have to backtrack a bit though, as far as I know, there is no Pokemon hiding in the trees on route 34, I don't know about route 35, because I have not been there yet. You can get a Phanpy on route 46.
Check the wiki entry for more info on Phanpy: http://pokemon3d.net/wiki/index.php?title=Pokémon_List/Phanpy
And for info on route 46, including the spawn rate of Phanpy during different daytimes: http://pokemon3d.net/wiki/index.php?title=Route_46
Check the wiki entry for more info on Phanpy: http://pokemon3d.net/wiki/index.php?title=Pokémon_List/Phanpy
And for info on route 46, including the spawn rate of Phanpy during different daytimes: http://pokemon3d.net/wiki/index.php?title=Route_46