It depends on each company as to who they employ. Generally though if the company can afford an outsider, they will, providing the dancer is very good.
Hungarian National Ballet was created in 1884.
Korea National Ballet Company was created in 1962.
Iranian National Ballet Company was created in 1968.
The most famous ballet company in Paris is the Paris Opera Ballet. In French, the name is "Ballet de l'Opera national de Paris".
The Royal Ballet was founded in 1931 by Dame Ninette de Valois. It became the resident ballet company of the Royal Opera House in 1946 and was granted a Royal Charter in 1956, becoming recognised as Britain's flagship national ballet company.
Hungarian National Gallery was created in 1957.
Hungarian National Philharmonic was created in 1923.
Hungarian National Bank , Magyar Nemzeti Bank
Korea National Ballet was created in 1962.
National Ballet of Rwanda was created in 1974.
Polish National Ballet was created in 2009.
American National Ballet was created in 2001.