Sorry I didn't see this until now. I never check this page and I don't get email notifications when a visitor message is left. I encourage you to use private message instead of visitor message; then users will get notified if they have that feature enabled.
As to your questions:
No rear locker available in the US from Mitsubishi on the gen III trucks, on on the gen II trucks. Also, I don't believe adjustable shocks are available. But, I was able to find some air bags for the rear coils (installs inside the coil spring). I had to make some spacers for them but they help for leveling a heavy load (like when I tow my trailer).
Otherwise, the OME heavy duty springs and Nitrocharger Sport shocks are the best option in the US.
Seating for 7: yes. There's a third row seat.
As to your questions:
No rear locker available in the US from Mitsubishi on the gen III trucks, on on the gen II trucks. Also, I don't believe adjustable shocks are available. But, I was able to find some air bags for the rear coils (installs inside the coil spring). I had to make some spacers for them but they help for leveling a heavy load (like when I tow my trailer).
Otherwise, the OME heavy duty springs and Nitrocharger Sport shocks are the best option in the US.
Seating for 7: yes. There's a third row seat.