Copper Hydroxide - found in many fungicides but look for trade name Cupro. Simple cheap and last time I checked Copper was Organic but I am not sure if the complete package would be considered organic. Either way it should handle your black spot and not harm the bees if used according to label.
10% of your customers are 90% of the problem.
You may think the grass is GREENER on the other side, but if you take the time to water your own grass it would be just as GREEN.