The 64-bit OpenGL import library is included in the Windows SDK and gets installed to %ProgramFiles%Microsoft SDKsWindows<version>Libx64OpenGL32.lib. The corresponding DLL is named opengl32.dll and is located in %SystemRoot%system32. The 32-bit version is also named opengl32.dll and is located in %SystemRoot%syswow64 on 64-bit Windows.
You can't load 32-bit DLLs in a 64-bit process, so whatever you read about x64 apps using the 32-bit OpenGL DLL was incorrect. There is definitely a 64-bit OpenGL DLL, but it has "32" in its name, presumably to make porting easier.
Ref.