I bought mine at Harbor Freight. My "table" is really an island in my kitchen and I need a clamp that is big to fit on it. They are some sort of a spring clamp. I have two sizes, and the larger of them works best for me.
Just in case they might work for you, let me see if I can find a site....
http://www.harborfreight.com/1-34-in...amp-69291.html
That is very close to what I use. Works fine for me. I have 8 of them.
Dina