Let me start this off by saying that I've always preferred sweaters, zip-ups and hoodies over t-shirts.
So, that is where my suggestion comes into play. Maybe a simple hoodie or zip-up with "We're Alive" on the front and "www.zombiepodcast.com" on the back. White lettering on black maybe. Something similar to the shirts.
So, either tell me what you think or just let this die into obscurity. Either way, I still want to buy something more.