As of summer 2022 there is an official RIPTA "Bus Is Turning" shirt available through Frog and Toad, which is a fundraising effort to benefit the House of Hope Community Development Corporation.
However, that wasn't the first shirt design to be inspired by the talking buses.
Since 2018, several instances of the shirt pictured below have been floating around Rhode Island. Note that this T-shirt design was in no way approved or endorsed by RIPTA, and at $10 a shirt I made basically zero net profit on these - this was simply one of my humble attempts at contributing some hilarity to the world:
I still have a limited stock sitting around. If you're interested in getting your hands on one, shoot me an email at ben [at] bennacar [dot] com.