I've ordered from UNCompany before, twice actually. Both went really well. I received both orders in about 3 days after I placed the order.
Just recently, I bought stuff from Tokyo-Model Company, I was sort of in the same situation as the OP, something was out of stock but they didn't tell me, so I was waiting for a few days wondering what's going on. I sent them emails and they told me the one item was out of stock and they are waiting for new stock to come in. A day or two after, they shipped everything and I received it in a matter of 2-3 days. I was worried at first, but they are a really good retailer.
As for UNCompany, I think they're still a really good retailer. Have you tried to ask for a refund on just that item? It seems retailers in Asia have a habit of not informing their customers that an item is not in stock.