I think there was a 7-C calc for Smaug, but I'm not sure if he can be scaled to the Maiar.
There is, he shook the Lonely Mountain. Strangely, the calc is on his movie counterpart's profile, but I'll link it
here for simplicity.
In any case, I think it's arguably safe to scale him to Balrogs and therefore other Maiar (specially Sauron). Balrogs are heavily implied to be greater in hierarchy than dragons, and rode them as mounts during the Fall of Gondolin. Besides, when Morgoth himself was overwhelmed by Ungoliant, a group of Balrogs went to the rescue, attacked the spider and drove it off. I'm pretty sure Ungoliant is mightier than any dragon. Granted the Balrogs were grouped, and Morgoth might have naturally helped, but that's nonetheless no small feat.
In fact, Smaug is not particularly large or powerful - for a dragon, I mean -, as he was stll young and not fully grown when he attacked the Lonely Mountain back then. So we can assume dragons like Glaurung and Ancalagon were (much) larger and more powerful, and safely scale this feat to Balrogs and other Maiar (though they for sure have better feats). More importantly, the feat should be scaled to dragonslayers like Túrin Turambar, Eärendil and to those who can fight and defeat Balrogs, like Ecthelion, Glorfindel, etc.
Speaking of scalling:
We have the Ancalagon feat, which is hard to scale reliably since he barely appears at all.
I can see the reluctance in scalling Ancalagon's feat, but we can clearly scale him to Eärendil, who killed him, and to Sauron, for "among those of his servants that have names the greatest was that spirit whom the Eldar called Sauron, or Gorthaur the Cruel." Being the greatest of Morgoth's servants, Sauron should reliably scale to Ancalagon without much issue.
Ancalagon has a single sentence worth of appearances last I checked, so it's a bit tough. Maybe figure out who scales to Earendil, who slayed him? Although I think he managed to use a Silmaril offensively there.
It's basically a certainty that Eärendil weaponized the Silmaril there, which makes scalling from him kinda tricky. I guess we could figure out who scales to who/what after we listed the relevant feats.