Not sure I am getting what you are saying Steve…
From just messing with it, the product number did not pull up anything, and there was no way I found to get an exploded parts diagram.
But, as Bill points out, go to the manuals page, and if you have the model number, you can get the exploded parts diagram, for example, my Santa Fe Atlantic is 8-5103, your GN Atlantic is 8-5107.
Under service manuals, for the 8-5107, you get this: https://www.lionelsupport.com/media/servicedocuments/138-5107Complete.pdf
You now have the parts list, and I think the “tie rods” are what I would call the side rod or connecting rod.
It’s on my page: 818-5102-580 - connecting rod (front to rear driver) AND on the pdf file above
From there you go to the parts menu, search the part, and put it in your shopping cart.
I searched that part, and it says “Available from North Lima Trainworks” … hmmm
https://www.nltrainworksinc.com/
Went there, and the only 818 part number I could find was the connecting rod for a Thomas, so you should email them, I guess.
Greg