I have been farming for nuggets and d. Bones for quite a while, but have kept no records, so all I have is from observation. In season one, I usually go through prov. 5 for nuggets and 6 for d. Bones. And, even though it has nothing to do with what you get, I only occasionally run a stage where they don’t show in the “what is available” screen. I just feel better seeing them, although I know they can turn up in any of them. That being said, I have also found that I get most of mine from season 2 prov. 1, 9, 8, and 7. No particular stages, since I go by what shows. I appear to find them in both normal and hard levels.
I have also noted that they appear, in any of those places be it season 1 or 2, in cycles. I have gone through them all and got nothing, time after time, only to return and farm successfully later that day or the next, etc. In the last week or so I went from having about 30 tornados to 80, farming just those provinces. At the same time, I have been using them on Titan fights at a rate of about 3 per set, not 3 per fight. So, I’ve overall gained. Same with the d. Bones, which I use in time stops and dragon bombs. I have about the same amount of themh, total of both, so they equal the tornadoes. I use them, at a little over 3 per fight set.
So, that’s my two cents for what it’s worth. Just depends on the cost ratio whether they are worth the extra cost farming in the more expensive area. I received one nugget in providing. 13 or 14, but don’t know where, since I am only now finishing those provinces. Hope this helps, but as wacky as the drop rates are I wouldn’t hold my breath.