Team UnLimbited supplies the Alfie Edition Arm and the Phoenix Hand:
You can download the OpenSCAD files and instructions for the Alfie Edition Arm or the Phoenix Hand and generate custom STL files that you can print and assemble yourself.
Alternatively, you can request a device directly from Team UnLimbited. But of course they have a waiting list.
Team UnLimbitied is a UK-registered charity, but they partner with e-NABLE US, e-NABLE France and the LimbBo Foundation - another UK charity.
assistive 3d printing is one of those uses that just makes sense. kids outgrow stuff so fast, being able to reprint or tweak an open design instead of waiting on some expensive custom part is huge.