I can't find any info on harvest festiva
Religous education, I presume. The term harvest festival is a recent invention of some Christian groups to promote an alternative to the Halloween festival, which is of pagan origin. All Saints Day is also a response to the pagan festival Halloween.
I don't think you will find much on Harvest Festival as a Christian celebration, other than what I gave above. It is an invention of "Christian" groups in response to a traditional pagan celebration.
In the US, candy makers are very supportive of Halloween, as it is a major event in their year. Like the floral industry, things which promote economic well being for certain sectors are hard to oppose. Consider flowers at valentines, for instance. And candies also at valentines...
What we need is a healthy food holiday. No alcohol, no fat, no flowers, with good times. I am not optimistic that will happen anytime soon.