When you say 'has come away' do you mean the carbon fibre has come off the backing plastic, or the entire trim piece is coming off the glovebox lid? If the latter, then it is held in by three torx screws so you may be able to repair the area that the screws bite into, then re-attach? If its the former, then I have no idea how to fix it other than to try some heat as you say - you may have to send it to a carbon fibre specialist for repair.
Used parts come up on ebay very occasionally - might be worth dropping a few breakers an enquiry email to see if they have any on the shelf.
Otherwise you're looking at new and I don't think they're available from dealers any more (but check with FRF) - however Viva Performance in the USA are still listing them - a full carbon fibre trim kit for $250 -
https://www.vivaperformance.com/carb...m-s70-v70-c70/
HTH