Unity doesn't provide an API to get all of the scenes in your build. This script will automatically (at script reload), or manually through the Assets menu, generate a text file that contains all of your enabled scenes in your build settings in a Resources folder. This can then be read at runtime and stored in an array.

SceneListExporter.cs

using System.IO;
using System.Linq;
using UnityEditor;
using UnityEditor.Callbacks;
using UnityEngine;

public static class SceneListExporter
{
    [DidReloadScripts]
    [MenuItem("Assets/Generate Scene List")]
    private static void GenerateSceneList()
    {
        if (Application.isPlaying)
        {
            return;
        }
        var sceneNames = (from s in EditorBuildSettings.scenes
                          where s.enabled
                          select Path.GetFileNameWithoutExtension(s.path)).ToArray();
        var path = Path.Combine(Application.dataPath, "Resources");
        Directory.CreateDirectory(path);
        path = Path.Combine(path, "scenes.txt");
        File.WriteAllLines(path, sceneNames);
        AssetDatabase.Refresh();
        /* Access scenes at runtime:
         * 
         * var sceneList = Resources.Load<TextAsset>("scenes");
         * var scenes = sceneList.text.Split('\n');
         */
    }
}