That's a pretty rare rifle, try calling Numrich arms, AKA Gun Parts Corp, they have a lot of used, one of a kind items and parts.
http://www.gunville.com/products/winchester-57-stock
$700
Aftermarket YES. Factory from Winchester NO!
The Winchester model 64 rifle in 30WCF caliber is a highly collectible Winchester rifle model. The gun was produced from the 1930s until the 1960s and came with factory iron sights and a wood stock.
remove the buttplate screws, and the buttplate. In the large round hole in the stock is the stock bolt. That is unscrewed to remove the stock from the rifle.
All depends on condition of the rifle,if the stock has been cut or not and what the caliper is.anywhere from $500.00- $1500.00
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Remove the stock and you will see what is keeping the bolt from sliding out.
not the original stock.
your winchester model 1894 pre-64 rifle is valued at between 500-600 dollars for a rifle in the condition that you describe.
Brownells has replacement stocks for the model 60. You can also go direct to fiberforce to get one.
Based on the serial number your model 88 rifle was made in 1958. The original stocks were checkered (I have a 1957 model 88), so the stock you describe is likely a replacement. The following link gives the dates of manufacture for many Winchester rifles:http://armscollectors.com/sn/windates.htm