Foam Backer Rod (Ann Arbor, Central Campus)

Recently I saw someone requesting Backer Rod, and I didn't know what that was. Now I am requesting some. It's cylindrical, foam to fill spaces before caulking over a gap or crack. Now I need some 3/8"-1/2 " Backer Rod to fill cracks before I caulk some gaps where my porch steps meet the vertical surfaces they meet at the ends. 6-8' is probably enough, but I'll be happy to pick up shorter lengths. Please let me know where and when I can pick up or if you can drop off 4 blocks south of the UM central campus.