It s from here. And so far there is no better VG sales number tracking in the world.
Remember the site doesn't track digital sales which seem to be making up a fair amount of sales now days on the platform, Bethesda also were the ones who said that sales on Switch are different to sales on other platforms in that they don't need as many sales on the platform to see a return. The business approach from how they're operating is the bulk of sales are on other platforms and the later Switch port only need to pay for it's own porting development which given how much more easier it is than prior Nintendo platforms wouldn't cost that much so the result is sales of around 100k or more are already covering port costs and making a return giving Bethesda extra money.
This works for Bethesda because they're not a company that relies on yearly release business models.