You can try the MTH parts department. They probably have some for the new LCT items, and they are a pretty good source of high quality parts.
Additionally, there are train parts vendors such as Jeff Kane of The Train Tender, George Tebolt, and Olsen Toy Train Parts. Jeff Kane has been excellent to deal with in my opinion, and they all have a ton of parts.
And, of course, you can watch ebay. They do turn up on occasion.
Unless you see a picture on ebay, etc, you'll need to ask if they are the plates with tabs or are they adhesive backed. The ones that look the best when installed are the ones that have the original style and are tabbed in place.