They get new clothing designs all the time. I know they've added more of the other 3 houses into the mix in the last few months (not just having a Gryffindor design but the same style of shirt/hoodie for Slytherin, Ravenclaw, and Hufflepuff too). I think they got a couple new prank/spell shirts in too, but I haven't been in Zonkos for awhile so I don't know if those are sold in the parks or if all the guests have just been buying them online and wearing them to visit. The house stuff is for sure Universal product.
