I'm guessing
You mean you have the shells and cushions, and need the swivel pedestal, the aluminum headrest connectors, and the steel arm-plates. best bet is to try Herman Miller or a Herman Miller dealer - but be warned, for what you will pay for the replacement parts you may as well buy a new chair.
You could try Graham Mancha...
You could try Graham Mancha in the UK
http://www.mancha.demon.co.uk/spares.html
If you need any help, please contact us at – info@designaddict.com