It would not be hard to make. You can buy the Irish heads from several suppliers, including Dixie GWs, and Track of the Wolf. The leather you can also order from several sources. Check the LINKS section at the top of the Index Page here, under Member Resources.
You don't want a Big, or LONG Shot Snake for this kind of thing. Anything that will hold more than 1/2 Lb. of shot is TOO BIG. There are 7000 grains to the lb. 437.5 grains to the ounce. Most small bore guns use an ounce or less of shot per load.
I made a shot BAG, with an Irish spout, that is carried inside my hunting pouch, rather than attached to it. I made my shot bag too big, and shaped like a "bottle". It carries more than a couple of pounds of shot. I need to cut down the sides of the bag, to make it long, rather than round, and resew the seams. I want a bag that will fit in the palm of my hand, easily, but be the length of my hand and extended fingers, to carry enough shot. That is what I will use squirrel hunting. :hatsoff: