@Bob posted:3rd Rail did run a K-class 4-8-2. They also did an N&W 4-8-0 (M class maybe?). Both are hard to find now. With lots of 3rd Rail stuff, you snooze you lose.
I can confirm that 3rd rail did produce the M class. Extremely hard to find. These are a highly coveted item (it seems that there is a sizable demand), hopefully they will consider doing another run of these in the near future!