Tindie is great for this type of stuff, if OP needs a platform. Though my experience is only as a buyer.
That said, if you have a 3D printer these days the process of ordering a board with full PCBA from PCBWay/JLCPCB/Aisler and printing the case yourself is pretty easy.
That said, if you have a 3D printer these days the process of ordering a board with full PCBA from PCBWay/JLCPCB/Aisler and printing the case yourself is pretty easy.