From Amazon: https://www.amazon.com/Alligator-Clips-Male-Adapter-Cable/dp/B011IZVZSG/
As sold directly by DX: http://www.dx.com/p/diy-dual-alligator-clips-to-usb-female-power-test-cable-black-red-62cm-371842#.WD2YzbIrLIU
As sold by DX's USA store (different SKU number for some reason): http://www.dxsoul.com/product/diy-dual-alligator-clips-to-usb-female-power-test-cable-black-red-62cm-901371842
Here's the USB male to test clips harness (to use for checking polarity hookup of the female adapter):
From Amazon: https://www.amazon.com/Alligator-Clips-Male-Adapter-Cable/dp/B011IZVZSG
As sold directly by DX: http://www.dx.com/p/diy-usb-male-to-dual-alligator-clips-power-test-cable-black-red-85cm-367144#.WDhynEbXuy4
As sold by DX's USA store (different SKU number for some reason): http://www.dxsoul.com/product/diy-usb-male-to-dual-alligator-clips-power-test-cable-black-red-85cm-901367144
Here's a super cheap, super simple alternative to the test cables (but would need some kind of safety protocol to use in an assembly process): https://www.amazon.com/Type-Breakout-Board-2-54mm-Header/dp/B01CEL1FW4/
Oh and astonishingly, DX has them for micro USB as well although they're presently sold out:
http://www.dx.com/p/micro-usb-male-to-dual-alligator-clips-power-test-cable-black-400890
