I stopped in at Streichers in Plymouth yesterday. I know that from time to time they have used firearms. These are generally LE buybacks. The long guns are kept in back and you need to ask what they have on hand.
I asked about shotguns. They have three used LE shotguns for sale. They are 870 Wingmasters with 20" barrel, bead sight, and cylinder choke. They have wood stocks and forend. These are normal capacity (4 + 1), 2 3/4 chamber.
I can't remember the price. I think he said $150 but he could have said $180. Either way, it's a good buy.
One of these would make a great Grouse gun. It could also be tricked out with the tactical stuff if one was so inclined.
If interested, act fast. They won't be there long.