シーン内のゲームオブジェクトをタグで検索できるスクリプトがUnity wikiにあったので紹介します。

FindSceneObjectsWithTag

以下は、自分用に少し修正したものです。Editorフォルダに入れて使って下さい。下図の様に、指定したタグのゲームオブジェクトを検索できます。（この例ではPlayerタグがついたゲームオブジェクトを検索しています）

FindSceneObjectsWithTag.cs

using UnityEngine;
using UnityEditor;
using System.Collections.Generic;

public class FindSceneObjectsWithTag : EditorWindow
{
	public string TagToSearchFor = "Player";

	public bool LimitResultCount = false;
	public int MaxResults = 1;

	public List<GameObject> Results;
	private Vector2 ResultScrollPos;

	void OnGUI()
	{
		EditorGUILayout.BeginVertical();
		{
			EditorGUILayout.LabelField("Options", EditorStyles.boldLabel);
			{
				GUILayout.BeginHorizontal();
				EditorGUILayout.LabelField("Tag : ", GUILayout.MaxWidth(50));
				TagToSearchFor = EditorGUILayout.TagField(TagToSearchFor);
				GUILayout.EndHorizontal();

				if (GUILayout.Button("Find"))
					Find();

				if (LimitResultCount = EditorGUILayout.Foldout(LimitResultCount, "Limit Result Count (Limit:"
						+ (LimitResultCount ? MaxResults.ToString() : "None") + ")"))
					MaxResults = EditorGUILayout.IntField("Result Max:", MaxResults);
			}

			EditorGUILayout.LabelField("Results", EditorStyles.boldLabel);
			{
				if (Results != null)
				{
					EditorGUILayout.LabelField("Scene objects found:", Results.Count.ToString(), EditorStyles.boldLabel);

					ResultScrollPos = EditorGUILayout.BeginScrollView(ResultScrollPos);
					{
						if (LimitResultCount)
						{
							for (int i = 0; i < Mathf.Min(MaxResults, Results.Count); i++)
								EditorGUILayout.ObjectField(Results[i], typeof(GameObject), false);
						}
						else
						{
							foreach (GameObject go in Results)
								EditorGUILayout.ObjectField(go, typeof(GameObject), false);
						}
					}
					EditorGUILayout.EndScrollView();
				}
			}
		}
		EditorGUILayout.EndVertical();
	}

	void Find()
	{
		if (TagToSearchFor != null && TagToSearchFor != "")
			Results = new List<GameObject>(GameObject.FindGameObjectsWithTag(TagToSearchFor));
	}

	[MenuItem("Tools/Find By Tag...")]
	static void Init()
	{
		FindSceneObjectsWithTag window
			= EditorWindow.GetWindow<FindSceneObjectsWithTag>("Find By Tag");
		
		window.ShowPopup();
		//window.ShowAuxWindow();
	}
}