There is a Forum Classified Section with guns listed for sale.
http://smith-wessonforum.com/guns-sale-trade/
But who knows what might be available at any given time. You may have to monitor the offerings for months before you see an M13.
You could always post a "Wanted to Buy" in this section:
http://smith-wessonforum.com/wanted-buy/
Again, no guarantees but you may get lucky.