that is a T shaped peice of alluminun which they have put in a break and folded the bottom part over to make that groove you can not buy a peice of alumminum that is already in that shape i am pretty sure . so your best bet would be to go to a shop that sells alluminum and has a break take that pic to them and get them to bend the T shape alumminum. i am a welder by trade and have never seen that shape before so that is just how i think they did it but i could be wrong