The tumbler is the last step and gives a polish, but it doesn't fix scratches or imperfections.
I bought my stainless steel shot from conniefox.com (she is local to me), but you buy it from most jewelry supply places - rio, thunderbird, etc...or, you can see if there is a lapidary supply near you they often have many of the same tools that jewelry people use including, tumblers, shot, burnishing solutions, etc...