I would think we have enough natural food but I just wanted to know what people think. Thanks
I like efmesch's idea. Last week I scattered seed bombs filled with aster seeds in the area around an out apiary. At home, I have slowly been converting the yard over to natives and honey bee friendly nectar producers.
I have discovered that honey bees are attracted to patches of nectar/pollen producers. A single plant will not catch their attention as readily as a patch. Not all sunflowers are created equal. Avoid the pollenless or double petal varieties.
Full sun is also key. I have reliable nectar producers that are in shade/part shade and the honey bees never work them.
The sources you have listed would seem to be sporadic. A continuous nectar flow is desirable. If there is a big enough gap in nectar flows, the bees could empty the supers and take the honey down into the brood boxes. There could be times you need to pull the supers off and offer supplement feed. In my area, an "old bee guy" preaches to watch your hives after the blackberries bloom as they could run short on food. He calls it a blackberry dearth.