big brother shirt suggestions

So my son is turning one in April and we are pregnant with #2. We had an idea of announcing our pregnancy at the birthday party and having a big brother shirt in a gift. Now I have been trying to find a cute shirt and I have not been able to find any. Does anyone have any suggestions of places I could check? I know target doesn't. I looked online at carters and couldn't really find any cute ones. I'm going to go to Walmart today and see.