Hard to get ahold of. If Lionel is going to make them part of their parts supply chain they really, really, really need to make the web site and customer communications better. How can they have nothing for sale on the "bay"??
I think you are over-characterizing the relationship there.
Lionel sold what was left of older parts back then so they would not have to deal with it. It was so long ago at this point, I would have to imagine today's Lionel has no cares (nor influence) for how NLTW is handling the business. I'm sure when they originally sold off these parts, there was at least some decent level of evaluation to see if NLTW would be a good fit in terms of being able to satisfy customer needs, but that was a long, long, time ago.
To the best of my knowledge the only connection today is the reference to some parts being "available from NLTW". I look at that as a bread crumb that is a step better than just seeing "unavailable", but it's just a possible shot at a part, not a guarantee.
I ordered some items from them on a few occasions in the past, but nothing recently.