A US person (for tax purposes) should not be dealing with a brokerage company operating outside of the US. The US government has decided that the only reason someone would do that is to evade taxes (although money laundering is a nice cover story) and punishes such behaviour with accordingly with additional paperwork and bureaucratic headaches.

A brokerage company operating outside of the US should still be sending you relevant local tax forms. If they are operating in a tax haven, well, maybe don't do business with companies operating in tax havens if you want your US taxes to be easy.