Wally.

Forget about wrecking yards.
I have also tried to find gearboxes from wrecking yards.
None can be found.
I will check tonight when coming home from work in a car magazine for some telephone numbers of places here that recondition gearboxes.Will mail it to you.
They will probably have some nissan boxes.
Your concern will be the cost to get it there.
And also if it is in good working condition.

My experience here is some people think they know how to fix or repair a gearbox only for you to install and get some gears running against each other when driving.
This is personal experience.
Ok I must admit this was some cheap backyard mechanic that I used to save money.
What a lesson I learned through that.