The last time I went to my local Dicks, all they had was the 12 and 20 gauge shells. That didn't help me much because I was looking for 16s. But, if you shoot any at all, you are better off just buying a reloader and loading yourself. I can still reload 12s and 20s for around $3.00 a box. Maybe less. I recently started shooting my 20 gauge Superposed at skeet and decided to reload. 20 gauge hulls were all over the ground at my club, so I didn't have any trouble getting 2-3 hundred in a week or two. Then, a buddy of mine came in with a 20 gauge reloader that I bought for $35.00. It works well enough to reloader a few boxes a week. I still have two 12 gauge reloaders and I can save a ton of money reloading my own. A flat is going to run around $50.00 and I can reload one for around $30.00. I probably shoot almost a flat a week. Earlier in the summer, I was shooting about 1 1/2 flats per week. You might not shoot that much just hunting alone. But anything other than 12s and 20s are going to cost you a fortune. So, you are probably better off just getting a reloader. Good luck.
Gander Mountain is very expensive I don't know how they stay in business. 