Hello mate welcome to the triumph family. You will need a Triumph rack to fit the top box which comes with a back rest that can be fitted to the box. Your best bet is to check out ebay, they come up from time to time although you may need to paint it to match up to your bike. There are a few breakers in the UK that will ship to the US but the boxes are few and far between second hand.
I can confirm that the pannier system is great for touring. The wife and I pack ours full and spend most summers touring France, Belgium etc.
Good luckwith tracking some down.
Ray.
