You can order it from your dealer, I did.
Af1 racing in the states do the kits, but you have to think about import tax or there is a German distributor on ebay, Im just waiting for them to get more stock of yellow.
Link is:
Aprilia RSV 4 Tuono Heckumbau rot / Soziusheck von RSV4 | eBay
I was quoted £450 from the stealers, some options for you to look at.