The shape of the spoiler means it won't create "huge" amounts of Downforce so I don't think the Mounts are critical. I suspect the current ones are a simple "L" shape. You could fabricate them from say aluminium angle and then bond them to the bottom skin from the inside. I would cut the originals off  and follow the EC "How to make a Carbon Fibre Bonnet video. (you could drill out the spot welds and use them on the new one)

I'm no pro, but I'd consider fabricating the mounting brackets out of metal and integrating them into the carbon layup. There are stresses and abrasion issues there that I don't fully understand. As a semi-functional aerodynamic device, the impact of failure would be considerable and for that reason I'd stick to metal for that part.