Sorry, I still cannot find it.
I use Visual C# 2008 Express to open GMap.NET.sln.
Then it prompts the below error:
"Solution folders are not supported in this version of the application.
Solution folder 'GMap.NET' will be displayed as unavailable"
So, even I compile the whole solution, I cannot find gmap.net.dll in Build folder.
It only contains of GMap.NET.Core.dll, GMap.NET.WindowsPresentation.dll, System.Data.SQLite.dll.