Is there any way to achieve a Flutter top snackbar?

You can set a margin using the device's height to achieve this:

ScaffoldMessenger.of(context).showSnackBar(new SnackBar(
    content: Text('Snackbar message'),
    behavior: SnackBarBehavior.floating,
    shape: RoundedRectangleBorder(
      borderRadius: BorderRadius.circular(24),
    ),
    margin: EdgeInsets.only(
        bottom: MediaQuery.of(context).size.height - 100,
        right: 20,
        left: 20),
  ));

You can use https://pub.dartlang.org/packages/flushbar

RaisedButton(
  child: Text('Show Top Snackbar'),
  onPressed: () {
    Flushbar(
      flushbarPosition: FlushbarPosition.TOP,
    )
      ..title = "Hey Ninja"
      ..message = "Lorem Ipsum is simply dummy text of the printing and typesetting industry"
      ..duration = Duration(seconds: 3)
      ..show(context);
  },
),