I have a 2012 2SS RS and bought the OE brace from GMpartsdirect on eBay for $150 shipped and it came with the bolts and took about 10 minutes to install.
Before this a guy at work with a 2012 1SS RS wanted a brace and went to the dealership to get one but couldn't find it in the catalog so he got the brace for the ZL1. After making a jig to keep the mounts in the proper place, cut it down and rewelded it to prevent the interference with the hood (a ZL1 brace is taller and will not fit under the stock SS hood). He was pretty proud of it until I told him about mine.
If they had looked up the part number for the convertible brace he would have been done in 10 minutes but it would have been more expensive coming from the dealership.