Most fabric and sewing stores sell white nylon belt strap material, from which you can make your own easily.
You'll need 5/8" to 3/4" strap material and a plastic slide buckle similar to the buckles used on most nylon packs and bags. Most sewing stores also sell these.
Assemble using hardware rivets. Use a red hot nail to burn the rivet holes through the nylon to prevent fraying, then rivet.
OR, have most any good shoe shop assemble your components for you.