system
A chat on subreddit /r/wallstreetbets
human
Sorry man, I thought they used to have it there, but now I can't find it.  I'm looking now and when I find it I'll share. 
  
 Basically you could find historical IV by day (I believe) for at least 5 years back, so you could definitely see 'normal' IV for a given time period.

gpt
Well thanks anyway, let me know if there's something. I only found something at optionseducation.org which has limited numbers and a vague low res chart  
  
 Doesn't explain why the calculator was off though