Well, if he doesn't have it, you're not going to get it, are you?
You can pout all you want, but the end result is the same.
Accept the refund and move on.
Just don't buy from someone who is dropshipping. When the factory is out of product, the retailer may not know and happily go on offering an unavailable product.
This is another reason not to become a dropshipping seller.
And of course, if the dropshipper's supplier is out of product, all that supplier's dropshippers will be out of product. So you won't be finding it until it comes back into stock.