how can you accertaina company's physical location?i.e in the uk you can ask their trade address, VAT and registration number(every company must have these elements and must provide them on its own website by law).what about in the us?

It's about the same, I guess. But not sure about posting trade address on the website (I'm sure it's possible to post a PO box as a trade address).

do you know what's the registry office (evwentually the federal one) webpage?i need some info on a company.

I'm not sure but my guess is that each state has its own..