Does anyone know where to get this wrench?

I have seen those too. Without the two posts welded on. I would try a plumbing supply store. I guess it would help a lot if we knew what those wrenches are called. Maybe somebody here knows and will share it.

 

Looks like its just a valve handle that's been removed.

You can use a crescent or pipe wrench too

 

I was thinking maybe its for using a pry bar for extra leverage in opening stuck valves, but I'm not a tanker driver, so I'm probably wrong.

 

On second thought you could probably use those posts to pry open a cam lock on the hose.

 

OK, I use a small pipe wrench for that. You mean a threaded fitting right?