Do you mean this pic below, mitsubishi call it the "boot flap scuff guard" it was sold as a genuine accessory but was sourced from a 3rd party back in the day (i think this is what you mean, it stops scratches on b/bar / on lower boot lip when sliding in heavy objects? if so they were available back in 04/05 for the wagon and sedan's, doubt if you would get one now from mitsi, however check out the ebay link below, they are very similar to what you are chasing, they may have even been the ones that supplied it to mitsubishi in the first place.
Also available was a separate edged carpet insert piece that fitted over the boot/rear wagon carpet as well, it should just Velcro on to your existing carpet when needed.
Think you may be looking at a custom job mate, wasn't aware they came with any boot lid carpet. And if they did I would assume either the VRX or Velocity would have it, if at all since they were the top models.
Alternative if you cant find one. Light weight car carpet from Clark Rubber and cut to shape either now or roughly and finish off when fitted. Glue some foam insulation to the outer skin area where visible, then glue carpet to all the braced areas and for extra grip get some scrivet (trade name?) plastic clips and secure the carpet with these as well. Be worth making a note of where the holes are in the braced areas before putting the carpet on but can be located later with difficulty and holes put in carpet and clips inserted to ensure better grip.