Bots

Check out your neighborhood.
You often might find chains of bot castles (usually lvl 28-29 or 36-39) that produce high amounts of ressources.
They are easy to raid and besiege and provide a constant flow of income. Usually they carry up to 50K of each ressource.
You can identify them by their names. Those names are often random letter and/or number combinations or russian names.
Those are the ones that I discovered but there might be other kinds of namings as well.
Just search for patterns.