A chrome split ring clamp about 4 inches wide fits around each fork tube.
There are 2 protruding mount points welded to the outside of each ring clamp.
The chrome mounting plates in the pic above bolt to the ring clamps.
The official Triumph 'Fixing' kit includes those fork clamps and I believe also the chrome plates in your picture are part of it, too.
So you are missing parts and nobody but Triumph makes the ring clamps.
Unfortunately I'm on the couch with back spasms, while my bike is in the shop at my work, since due to the back issues I had to get a ride home today....:-(
I can't get you any pictures at the moment. Go to www.puretriumph.com look under windshields for the Rocket and it will give you info on the fixing kit
I was not entirely accurate in my description.
From the picture you can see there are 2 clamps per fork tube, not one,
each having a protruding mount point.
It fits all not-touring Rockets.
Cough up the $90 and be happy ;-)