AcyMailing has the universal filter plugin for that:
www.acyba.com/acymailing/309-acymailing-...universalfilter.html
With the advanced query mode, you can write such query:
SELECT u.user_email FROM #__hikashop_user AS u JOIN #__hikashop_address AS a ON u.user_id=a.address_user_id WHERE a.address_country='country_United_States_of_America_223';
and that should allow you to get all the US users with such filter and you can combine it with an action to send an email to them or add them to a specific list for later.