Most any gunsmith should be able to handle detail stripping a 336. I'd suggest that you do it yourself. All you need is a good set of screwdrivers.
Disassembly instructions....
http://www.marlinowners.com/forums/index.php/topic,26786.0.html
Since your 336 is so old, its probably well broken in and only needs cleaning but here is how you "tune up" the action
http://www.marlinowners.com/forums/index.php/topic,58735.0.html
Search on youtube for Marlin 336 disassembly....there are a couple of videos showing you exactly how to do it.
Last edited by RJY66; 06/16/11.