I have several of these freight trucks that have the same issue. Apparently, they've been dropped and broken the coupler right at the shaft. I couldn't find a part number for either the truck or the coupler, but they're on stuff that was made around 2006. The second picture is why I need them, I have two of these that have the same break right at the shaft. If I could find just the coupler, that would be keen, but I'd also buy the truck if that's not available as a separate item.
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John, I have a bunch of MTH couplers of the style shown. However mine appear to have a longer coupler shank than shown above. The shanks on mine are 0.83" (21mm) from the center of the shaft hole to the back of the knuckle casting. Let me know if they will work for you.
Sounds close enough! There look like .75", I don't know anyone would notice less than .1". 
They just have to be the ones with the little lever that sticks in and activates the knuckle as in the first picture.
Note the tin lever sticking in the slot in the knuckle.
Do you have the tin lever lever as well. The only issue I see is the slight difference in length may need a different lever, hard to tell without seeing them.
I'll take some photos of what I have and post them this evening.
I have these. The shank is about 13/16”.
This is what I have. I can disassemble or send as-is and let you do it. Let me know how many you want (I have a bunch).
Bob, that looks great, I'll send you an email. 
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