Ordered mine from BMW dealer, about 5 years ago for about £65. You will need the extra long pop rivets from BMW to fit the hinges.
I tried various repairs but didnt find a long term solution so went back to the source.
If you find a 'half' on ebay, check the part number inside yours against the one for sale. One I found said it was for an R1150GS but the part number was diferent and was not for my bike.