The best place I found so far is here.
http://www.gunstocksinc.com/web%20pages/Plate%20Pic's/Stevens%20stocks%20images%20&%20Descriptions/Savage%2099%20shotgun%20butt%20pistol-grip.htm
I have searched the internet for 5 days now searching for the most accurate aftermarket model and this seems to be it. Every other place I have found is not a true replica (they always seem to change the pistol grip bottom).
The one shown is about $45.00 (it is their cheapy model, American Walnut - nothing really fancy - just straight grained) but if you go to the homepage, you can get upgraded wood (under wood grades). There are 4 different grades that will cost anywhere from $45.00 to in excess of $350.00.
I have not decided which grade I am going with, only that I will buy from this guy. I spoke with him today and feel confident that his workmanship is above par.
If you decide to upgrade to a 'better' wood, you need to call them directly to let them know. You can only get the base grade on the internet.
If you find something else, please let me know. Like I said, I have been to around 30 internet sites and this place seems to be the best.
