Unprocessed wheat and oat bran can be added to all sorts of meals to increase their fibre content. The bran of a wheat or oat kernel is the rough, outside coating of the kernel and while it does not contain a lot of nutrients, it is an excellent source of fibre. The bran is removed from the kernel during milling and it is often packaged separately to add flavour and fibre to baked goods.
Look in your local health food stores or the health food section of your local grocery store. Many health food stores specialise in selling unprocessed products both packaged and in bulk. Grocery stores often have a section of the store devoted to health or bulk foods, so looking there is a good place to start.
Ask your local grocery store or food cooperative if they can help you find a source of unprocessed wheat and oat bran. They will have connections with large food distributors and may be able to connect you with the right company.
Purchase wheat or oat bran online from places such as Hodgson Mill, Purcell Mountain Farms or Bob's Red Mill. All of these stores have oat and wheat bran in varying quantities. Many health food stores have online stores and can send you the amount you need.
Contact a flour mill in your area and find out if they sell unprocessed bran. This could be an excellent source of a large amount of bran if you need it.