I upgraded from a R1150Gs Adventure to a R1200GS. I had a Touratech Xenon Auxiliary Headlight as they call it that needed a bracket for the ballast to fit the 1200. Barry Maas of Touratech helped me out with a part number, 05-040-1527-1 which is the part number for the right side (offside) ballast mounting bracket. This bracket carries the ballast under the right hand side of the beak where it meets the black trim carrying the BMW roundel. Although the bracket is for the Touratech ballast, it would be no trouble at all mounting a different sized ballast to it.
Touratech make the brackets for both sides of the bike, the only difference is one is the mirror image of the other so, if one was to buy one bracket, with a few tools it would not be difficult to make the other side bracket with one as a pattern.
You might like to send an email to Touratech AG Germany attention Barry Maas just to confirm the part number but you may need to order the part via Tourtech UK.
Brian.