Wow, this is a blast from the past. lol
I bought the parts from lingshondaparts.com in the UK. You will need a different mounting bracket that attached to the box but the bottom metal mount that attaches to the bike stays the same. Here are the part numbers from when I ordered it:
1 x PFKL2164515, 45L TOP BOX PROMINENCE RE - 08L72MGED41ZB
1 x PFKL2153092, KIT,CARRIER BRKT - 08L73MGED40
It's been a while so hopefully they still have availability. The option was never made available in the US unfortunately.