I have a used Ultergra SL rear that is in perfectly working condition. If you are really interested I could email pics. I also have a new sram force double front braze on, not what your looking for but its just sitting around and I would sell it cheep.

Try ebay...they have many and are very cheap!

i have a brand new in box Braze on dbl Dura Ace 7800 listed on the classifieds..$65 shipped