1940's
The model 5100 Stevens shotgun has a plastic stock
$100-$175, depending on condition.
Your Stevens model 240 was made from 1940-1945.
model 94B Stevens plastic stock was mfg in 1950. Stevens uded letter code starting with A in 1949 until P in 1969.
Try e-gunparts.com
it's probably a model 5100. the tenite (plastic stock and forend) as it was called was likely made sometime around wwII, because of a shortage of wood built gunstocks and forends
Go to a fashion show, knock on the door of the model Stevens and give him 77 kisses.
According to the Blue Book, all Model 94's were made from 1926 to 1945.
That may be tough since the tenile plastic stocks tended to break and there have been no aftermarket replacements. Try Gunparts Corp or Jack First.
usually the stock is behind and the forearm is in front of the receiver.
Currently they are bringing between $200 - $400 depending on the condition.
Try searching for a Savage model 620A or Stevens 620 stock on ebay, or gunbroker.com. The model M060 Westernfield is a Stevens 620, while a Westernfield model 60 is the Savage 620A