How to call a randomized loot table method again from within itself to prevent duplicates in Unity?

Question

I have a basic loot table with weighted drop rarities. I am trying to make it so that when the game starts, it will re-roll if the item already exists in a duplicated list.

I've created an empty list in shopManagerScript and am adding each instantiated item to that list. Then I would like to check against that list to see if the item exists. If it does, I want to re-roll again. If it doesn't then go ahead and instantiate the item.

This current code is executing endlessly however, and is crashing my game.

public GameObject shopManager;
public ShopManager shopManagerScript;

[System.Serializable]
public class DropItem
{
    public string name;
    public GameObject item;
    public int dropRarity;
}

public List<DropItem> ShopItemPool = new List<DropItem>();

private void Start()
{

    shopManager = GameObject.FindGameObjectWithTag("ShopManager");
    shopManagerScript = shopManager.GetComponent<ShopManager>();
    SpawnItem();
}
void SpawnItem()
{
    int itemWeight = 0;

    for (int i = 0; i < ShopItemPool.Count; i++)
    {
        itemWeight += ShopItemPool[i].dropRarity;
    }

    int randomValue = Random.Range(0, itemWeight);

    for (int i = 0; i < ShopItemPool.Count; i++)
    {
        if (randomValue <= ShopItemPool[i].dropRarity && !shopManagerScript.shopItems.Contains(ShopItemPool[i].item.ToString()))
        {
            Instantiate(ShopItemPool[i].item, transform.position, Quaternion.identity);
            shopManagerScript.shopItems.Add(ShopItemPool[i].item.ToString());
            return;
        }
        else
        {
            SpawnItem();
        }

        randomValue -= ShopItemPool[i].dropRarity;
    }
}