You can get those parts either from your local dealer or online.
I once ordered some parts from mrcycles, it worked out fine and shipping was very reasonable.
You can just pick your parts from their '"exploded'' views.
For instance, for the exhaust gaskets, see:
http://www.mrcycles.com/oemparts/a/s...723a63/muffler
or:
http://www.mrcycles.com/oemparts/a/s...0723a57/gasket