The most interesting comment to me was about the National Retail Federation 4-5-4 calendar. That calendar was hard to understand, so I made a visualization of it. I also implemented the other calendar types people were asking for.
I did find the SEC dataset of 10032 publicly traded companies [2][3], but have not finished implementing a search for symbol yet.
[1] https://news.ycombinator.com/item?id=43162340
[2] https://www.sec.gov/data-research/sec-markets-data/financial... (SUB data set, field `fye`)