when did the company establish?
August 2006.
Honda Aircraft Company
Honda Aircraft Company was formed as a wholly owned subsidiary of Honda Motor in August 2006 under the leadership of HondaJet designer Michimasa Fujino. 
who manufactured the honda ha-420 hondajet? The Honda Aircraft Company. when was it manufactured? 1999.
wiki:11302753
Honda Aircraft Company [SEP] Introduction
Honda Aircraft Company is an aircraft manufacturer headquartered in Greensboro, North Carolina, responsible for the production of the HondaJet family of aircraft. Originally a secret research project within Honda R&D, Honda Aircraft Company was formed as a wholly owned subsidiary of Honda Motor in August 2006 under the leadership of HondaJet designer Michimasa Fujino. Honda Aircraft Company began delivering aircraft to customers in late 2015, and by the first half of 2017 its HondaJet had become the top-selling twin-engine light business jet. Honda Aircraft has introduced a number of innovations in general aviation aircraft, including an over-wing engine mount, natural laminar flow wings, and carbon composite fuselage.