<p>Looking for code samples to access a memory map file in C#</p>

You can take a look at
this CodeProject article
which shows a simple array over MMF implementation using
Winterdom's FileMap library
- basically a wrapper around the Win32 APIs for memory mapped files.
Caveat emptor: 1) I have not used FileMap, so I can't vouch for it; 2) FileMap is under LGPL, if the licensing terms are of any concer of you.
You can also search on
http://pinvoke.net
for the P/Invoke definitions of the corresponding Win32 APIs and roll your own implementation.