The webbing straps can be bought at Seattle Fabrics at the store, online, or by catalog. I used the crushed walnut shells found as Lizard Litter at a pet supplies store. This same crushed walnut shells were used in some gun rests used for a 4-H Shooting Sports group.
If you are ever in the Seattle area, it is worth a trip to Seattle Fabrics. The catalog is a fun read. Anyone who ever sews outdoor items can benefit from the catalog. I have bought some nice lycra knit there for cycling tights, also some polar fleece.