Even if they did have it, this would (rightfully, IMO) probably fall under "must call" and "send in defective one for exchange".
Sort of like for some shells/chassis. - How many people would try to buy just one full engine of an F3 set and then all the different shells so you can have SF, NYC, PRR, etc, right?! (just an example)
Otherwise LOTS of people would love to make their own with the unique parts. Not the way the importers (nor overseas manufacturers) play the game these days. A lot of the parts Lionel does have they get by disassembling extra full pieces they order with the batch of orders.
-Dave