Hi Howard,
bakelite-bodied FMs are not too seldom seen on ebay.com, it looks they sold like hot cakes in the USA, so I think you don't have to wait too much for getting one. SP, T&P, C&NW and Monon liveries (introduced in 1954) are quite rare and usually expensive, however WP and SM (kit) are more common and much cheaper. The cheapest option are SMs when assembled and custom painted, which can be easily reverted to original (undec) stripping the paint.
The most safe way to detect a bakelite-bodied FM even in bad pictures is by checking the rear wall bottom edge, below the door, which must be STRAIGHT, i.e. there is NO SLOTTED EXTENSION to hold the metal frame (which is screwed to the body). In case, you can ask the seller to confirm that there are screws/holes securing the bottom to the body (six - four at corners and two near the tank).
Good luck,
Dodi