As you have found, it is unavailable from Lionel and probably everywhere else... However, it would seem to me a trip to the dollar store at this time of year would net you a set of headphones (for the connector), LED holiday lights, and a miniature Christmas tree that you could bash together with a current limiting resistor and diode of sorts...
For Example:
https://www.dollartree.com/cob...ge-collection/296612