The stuff you are looking for is Urethane foam, mostly sold retail through upholstry shops. It is available in a variety of different densities and weights. Ask for foam sheets which have been through a "convoluting" machine. These sheets have been cut in a deformed manner which makes them "bumpy" and can be cut not only to cushion but to "grab" the items you wish to protect. The stuff comes in large loafs called buns which are then cut down to the size the customer seeks. Any large upholstry shop should be able to get you all you want.
Mark