Hi
Agree with James, parts can be found. Getting in contact with those such as Don Nieser, Yingling and Prefferd Airparts just to name a few.
It comes down to what your replacing, interior plastics I have all new from Plane Plastic's, and have recently worked with them to rebuild their lower clamshell door tooling for a better fitting plastic trim.
Don has been great with ribs and other small panels I have replaced as has Prefferd Airparts. Yingling is very good with many of the small Cessna parts, control cables etc.
Prices are not too unlike other aircraft for parts, somethings are reasonable, some are not.
Ernie Martin has a great helpful guide which I have found very good in assiting me, check out Ernies post's.
Keep in mind I have been completing a total ground up restoration of a 74 Skymaster, not just general maintanence. This being the case I have been on the lookout for a little more than the normal.
And we are almost done!
Dave