I think you will have to buy a blank and make a stock. Your customer might not be happy with the price, but it is extremely unlikely you will find an original or that it would be in good condtion and fit if you did.
A friend of mine has a shop in Wilmington Delaware and makes great stocks.
Mike Delgrosso of the Gunstock Shop. (302) 571-1656, 806 N Union St, Wilmington, DE 19805
He is very reasonalbe in his prices and does excellant work.