400 km/h isn't very fast, but here's a couple:
https://www.beechcraft.com/military/..._trainers.aspx
Embraer Defesa & Segurança
What's the budget? And why the 2 seat and retractible gear fetish? You don't normally see the landing gear and rear seats while you are flying. If 4 seats and fixed gear are ok there's the Corvalis
Cessna TTx - The fastest fixed gear single engine plane in the world
or the Mooney Acclaim
Acclaim Type S » Mooney International Mooney International