The King Arthur Flour Co. carries a lot of specialty flours and may have the brown bread flour which you seek. Check out their website at http://www.kingarthurflour.com/ .

They also have some specialty flavors that may help you capture that butter flavor without the extra fat. One is called “buttery sweet dough flavor” and the other is “princess cake flavor”. They are both those flavors that bakery-baked goods have but you can’t seem to replicate at home.

Also, I think you may be able to steam this cake in a crock pot, assuming you have a can that fits your particular crock.