if you have the mapping toolbox then you can use tools such as gshhs
But if not then you can use the tools in m_map which is an excellent package
There are many tools (and examples) in that package which you can use.
Else you could get the coastline from the NOAA Coaslie extracter
http://www.ngdc.noaa.gov/mgg/coast/ and make your own patch.
Or you can use the tools the WHOI Sea-Mat Page
And look at the code under the map_stuff link which sends you here
Lots of choices for you to try.
Good luck, Mark