Well, since the bike in question is 36 years old and had a relatively short production run; I doubt finding parts would be easy.
To get parts; you'll have to salvage from 'deceased' CB400s and in my 30 years of existence; I never caught the glimpse of a CB400 in Pakistan or abroad. The bike is a very rare bird...
P.S Thumbs-up for reviving an old thread instead of starting a brand new one!
Good Luck with your quest!