A Sketch plugin that lets you create and specify how many duplicates of a layer you want.

sketch-duplicate.sketchplugin

var input = [doc askForUserInput:"Total copies:" initialValue:'']);

var count = parseInt(input);

var quit = input == null;

while (count != count) {
  if (quit) break;
	
  input = [doc askForUserInput:"Please enter an actual number for copies:" initialValue:''];
  quit = input == null;
  count = parseInt(input);
}

if (!quit) {
  for (var i=0; i<selection.count(); i++) {
    var layer = selection[i];

    for (var j=0; j<count-1; j++) {
      layer.duplicate()
    }

    print(layer);
  }
}

How to install

1. Click the Download Gist button to the right.
2. Unzip the .tar file it downloaded.
3. Move sketch-duplicate.sketchplugin to ~/Library/Application Support/com.bohemiancoding.sketch3/Plugins

Using the plugin

1. Select the layer you want to duplicate.
2. Click on Plugins > sketch-duplicate and specify the total layer count you want.
3. Profit