Of course you can spend $$$ to buy specialty flours but why would you want to when it's so easy and much cheaper to grind your own?
Whole grains will keep at room temperature indefinitely. Only grind as much flour as you plan to use since freshly ground grains get rancid very quickly. Once ground they can be stored in an airtight container in the refrigerated for up to one month. Most grains can be ground using a strong blender or food processor. A designated coffee grinder will also work but that would take a lot of time grinding such small amounts. If you find you're grinding a lot of flours consider investing in a hand or electric grain mill.
These are the flours I use most often but you can grind practically any grain, nut, or bean to make flour.
Purchase old fashioned rolled oats such as Quaker or the store brand. Pour the rolled oats into a blender and secure the lid in place. Blend or process on low speed in 30-second increments stirring to remove any oats that may be stuck to the sides or bottom of the container. Continue blending or processing until the oats are the same consistency as flour. Don’t use quick oats which are precooked since cooking them again will create a mushy texture. Steel cut oats can be ground but will result in a coarser flour. 1 ¼ cups rolled oats yields 1 cup oat flour.
Purchase pearled barley such as Quaker Medium Pearled Barley. Pour the pearled barley into a blender and secure the lid in place. Blend or process on low speed in 30-second increments stirring to remove any oats that may be stuck to the sides or bottom of the container. Continue blending or processing until the barley is the same consistency as flour. 1 ¼ cups pearled barley yields 1 cup barley flour.
Potato flour, ground from peeled, dried potatoes provides a soft, moist texture, makes dough easier to shape and handle and increases its shelf life. Add potato flour to the dry ingredients in your recipe and whisk together before adding directly to liquid or it can clump and make lumps.
You can grind instant mashed potato flakes to make your own potato flour in a blender. Read the ingredients in order to choose an all natural or organic brand to avoid extra additives your dog doesn't need. When baking breads it's recommended to replace 1/4 cup of regular flour with potato flour. Making Kirby's treats I've successfully used just potato flour since he enjoys the dense, chewy texture which lets the main flavors come through. 2 cups ground potato flakes yields 1 cup potato flour, 1/3 cup potato flakes = 1 medium potato