You aren't likely to find one in the size you listed.

How do you intend carrying it? If the lock is at the bottom it will not back down even if loose.

I have a few older largish non-locking carabiners that I use for attaching stuff to bags. The gates have never opened inadvertently, probably because of the fairly strong spring keeping them closed. One I really like is very similar to the Black Diamond Light D Carabiner.