The rack with rider's backrest (Driver sissy bar with pillows and luggage rack
6087 FRG) is the sixth item below Euro 208.15 Tax exempt outside EU, Euro 247.70 with 19% VAT for Euro area buyers.
Fehling
Rocket stuff is at the bottom of this Triumph models listings page. Click on the camera to see the photo links. Normally if a retailer anywhere in the world sells one they will sell other of the items below.
Triumph Performance Parts here in Oz . Motea and others in UK, NewBonneville in the USA
NewBonneville and many more worldwide retail Fehling products etc etc.
Fehling
For Triumph Rocket III Roadster, (C23XB / ROAD) 2010-
Items: Suitable for:
Order number: EUR without VAT EUR incl. 19% VAT
I got a couple of pairs of front crash bars and the Driver Sissy bar from different sources. One pair of front bars were about Au$305 delivered to Australia but I doubt you will find them that cheap now. The Driver Sissy bar was a little more from memory.

Guard, extra large version of 38 mm tube, 2 pcs.
6082 DGX TR Rocket III Roadster Pair 190.80 227.05

Baggage Holder
6083 P TR Rocket III Roadster Pair 69.45 82.65

Rear rack
6084 RR TR Rocket III Roadster piece 95.50 113.65

Solo Rack
6085 BR TR Rocket III Roadster piece 92.90 110.55

Sissy bar made of tube with cushions and luggage rack
6086 RG TR Rocket III Roadster piece 168.40 200.40

Driver sissy bar with pillows and luggage rack
6087 FRG TR Rocket III Roadster piece 208.15 247.70