Aprilia Atlantic 500 parcel rack
By sheer good luck, I managed to acquire a great looking retro-style parcel rack for my Aprilia Atlantic 500 a few weeks back. Whilst talking to my dealer about some of the accessories that finally became available in the last few months he commented that he'd actually ordered one in by mistake (I guess he was after the rear box mount) and so I blagged it at pretty much cost price.
As I know these things are traditionally a pain to track down, quoting the Aprilia part number of 8792301 will probably help.
Incidentally, the entire Aprilia accessories 2004 catalogue is available online should you need to find other parts (although, expect the usual Aprilia premium prices in most instances).