GUISkin.FindStyle

説明

GUIStyle 名で GUIStyle オブジェクトを検索します。ない場合は null を返します

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    public string aStyleName = "A Style I have";
    void OnGUI() {
        if (GUI.skin.FindStyle(aStyleName) == null)
            Debug.LogWarning("No style named \"" + aStyleName + "\" could be found");
        
    }
}