There's no merchandise available yet, but this is where I'll be selling an epic Wikipedia Golf cheat poster showing the relationships of a ton of common articles if/when I have sufficent bored time to make it. I'd also make some T-shirts available if there's demand for them.
If you'd be a buyer, email oracleofwikipedia (at) gmail (dot) com and tell me. One or two enthused emails would probably be enough to get me to make it a priority.