The plastic battery cover and styrofoam battery piece should be easily available at any salvage/junk yard. As far as the rear mat goes. Lloyds Mats sells custom built mats for the trunk, I have mine built with black carpet, Orange binding and stitching, and its embroidered with CAMARO in the center. Its really nice plush carpet too.
Battery cover tray
https://www.ebay.com/itm/385205636164
Battery foam
https://www.ebay.com/itm/31420748217...90.c101224.m-1
Lloyd mat
https://www.ebay.com/itm/11607682685...Bk9SR8zNvN2YZA