If you don't receive a response here, you might check an office supply store for rubber or foam pencil grips. I've heard they work quite well as hook grips but have not tried them myself.
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Life isn't about waiting for the storm to pass ... .....it's learning how to dance in the rain!
I don't have any extras, but I use these: http://www.joann.com/joann/catalog.jsp?CATID=cat2873&PRODID=prd12584 I get them at the Joanns store near me. You have to cut one end off to slide th ehook through, but they are really nice, not too big and intrusive. I've also seen them at my LYS.
I've also used plain tubing. All you have to measure with that is the inside diameter and how much it stretches. Since I'm allergic to rubber I try to find the plastic kind.