I used to make bran muffins with Nabisco 100% bran cereal. I have found that Nabisco sold to Post, so the Post 100% bran cereal looks the same and should work.

Here is the original recipe from the old Nabisco box:
2 C. Nabisco 100% bran (use Post 100% bran now)
1 1/4 C. milk
*1 C. all-purpose flour
*1/3 C. firmly packed brown sugar
*2 tsp. baking powder
1/2 tsp. baking soda
*1/4 C. Blue Bonnet margarine, melted (ugh!)
*1 egg, beaten

*I would recommend substituting some of the ingredients, following another bran muffin recipe I have to make this more healthy:

Whole wheat flour instead of all purpose,
Non-fat or low-fat milk instead of whole milk,
Honey(or molasses)in place of the sugar
1/2 tsp. instead of 2 tsp. baking powder
2 Tbsp. Canola oil, plus 1/4 C. applesauce in place of the margarine--ugh!)
Use 2 eggs, beaten.
I also add 1/4 C. chopped raw almonds (a coffee grinder works well), and 1/4-1/3 C. dried cranberries or raisins.
And, I may start adding a little ground flax-seed as well.

Bon appetit!