The Hayashi Trading Company is our sole agent in Japan.
Literal
Hayashi-Trading-Company [subject-が] Japan [in-における] our-company [of-の] sole agent [copula-である].
~における ('in, at, regarding') is a formal equivalent of で or での, especially in formal contexts like business and academia. 代理店 ('agent, agency, dealer'). ~である is the formal copula. Business/legal register.