Tower clamp inserts....where to purchase

I recently bought some tower speakers and the clamps seem a little to large for the diameter of the tower. I added some weather stripping from homedepot in between the tower and the clamp but it doesn't seem to work...the stripping isn't dense enough and they slip a little. Anyone have any idea where I could buy something like the "Monster Tower Universal Inserts" They say they only work on monster tower clamps so I don't won't to shell out $50 for nothing. I figure there is something I could buy at a hardware store but haven't had much success. Anyway, any help is appreciated.