Try:
http://www.traditionsfirearms.com/eShop/10Expand.asp?ProductCode=A1308.
If that doesn't work, try building it yourself. Here's a picture and some dimensions:
Dimensions:
Base is 6 1/2" long by 3 1/2" wide by 3/4" thick
Upright is 3 7/8" high by 3 1/2" wide by 3.4" thick
Front edge of upright is located 3 7/8" from the front edge of the base; if the upright is folded down it fits within the dimensions of the base.
The notch in the upright is 1 3/8" deep, the upper opening is 1 1/2" wide at the top by 7/8" deep; the lower opening is 1" wide at the top by 1/2" deep.
The notch in the base is 7/8" wide at the front and begins 5/16" back from the front edge of the base. It is 2" long. Depth iis 1/4" in the center at the front edge tapering to zero at the back edge and on either side.