I also own a Super C8 Plus SCT, fork mount.

First the ONLY dealer who has parts I know of is:

http://ngc1514.com/Celestron/celestron.htm

he is high, but he bought out ALL of the parts from Celestron for the original scopes.

Second, as to your focus issue, sounds like the scope needs collimating.

I have a complete list of everything I know about the care and use of Celestron SCT's

http://c8astronomy.home.comcast.net/html/c8.htm

Hope this helps

Bill

c8astronomy@comcast.net