I use those also, but I got mine from Joann Fabrics and Walmart. They are so much cheaper there. I probably have about 6 of them. I also have a metal dish type thing that I got at a tool sale. I guess it is used to hold bolts so you don't lose them. I got me two of them and now I have two magnetic "bowls" 6" in diameter.
I must add that I use them for more then just making quilts. I also do upholstery work so they are really in demand for me.
Barb