try this guy, he normally has bits of 2 strokes around back and he sold a ns400 not so long ago...

https://www.reservoircogs.com/Home.aspx

also, i cant find them on the net for some reason (ill try and dig the number out its a brand new shop they have just moved, now part of the car showroom in fengate). Have a look for the Honda Dealer in Peterborough. he is selling a NS 400 and has lots of parts, you need to speak with the manager its his personal bike. If he has a rad, he might let it go for a decent price!!!!