Snipe,
Some good advise given here. You may also want to consider the english style shot & powder flasks that Track of the Wolf carries. Both are adjustable to the load that you may want to shoot and are for shotgun.

If you have a local supply of black powder, I would recommend it.
I find that it is generally less expensive than the substitutes.
When you go to purchase wads, I would recommend using one size larger overshot in a double gun. It will help keep the second charge from moving during the recoil from the first barrel.
If you need help, by all means give me a call and we'll get you started out on the right foot.

Craig
http://www.circlefly.com