You pretty much need to order slugs online. You are not typically going to find any in stores and if you do they will be charging a premium. My 870 liked the 2 3/4 1 oz fiocchi slugs better than the brenneke. They run about $9 for a box of 10. My shotgun really likes the hastings 2 3/4 magnums but hastings went out of business. I think I am going to start reloading them.
I shot the brenneke Rottwiel slugs outta a smoothbore 870 20ga. WHatever the bead covered on the end of the barrel, is where the slug would hit. Never seen another slug shoot that well. But the recoil outta 3" was severe to say the least. It was not fun to shoot!!