If I remember correctly you can go to
http://www.eibach.com direct or they distribute to your local dealer via White Brothers. Now I am making a huge assumption that the shock body on the '82 (KYB) is the same as the '83 (Showa). The 883 spring is a little tight so you might want to get the dimensions of the existing KYB spring and compare the 883 dimensions from the Eibach web site. The part # is 883-00XX where XX is the rate in kg/mm. So my .67 kg/mm spring is 883-0067. Check out
http://www.racetech.com where they have bike specific spring rate suggestions.
IMO, you can rebuild the motor yourself if you are willing to invest in a rotor puller, clutch holder, case splitter etc. The tricky stuff is splitting and re-balancing the crank. I have used
http://www.racerstoystore.com but there are others.
BTW, don't
rush to re-valve either forks or shocks until you have the right springs. The Showas had more adjustments but I have heard the KYB forks for instance worked just fine. New springs - if needed - and then play with the adjustors and oil height might be a cheaper start.