Here is a posting from someone who says they have ported the amf deserializer and serializer from AMFPHP to C++ but I didn't see any code.
http://osflash.org/pipermail/osflash_osflash.org/2005-July/001560.html
Maybe take a look at some of the opensource flash remoting implementations for .NET. You may be able to use their AMF serializers and deserializers.
https://www.flashsec.org/wiki/Software#.NET
You could also try porting the AMF serializers and deserializers that are in BlazeDS to C++. These are in the flex.messaging.io.amf package.
http://sourceforge.net/projects/libamf/files/