Tim Goldstein at A2Z CNC sent me one of his endmill holders they make for the Taig Milling Machine.
Functionally as good as the ones made by White Wolf Airsmithing, the A2Z is a more polished (and slightly more expensive) product. What I especially like about it is the 7/8" hexagonal portion that allows you to use a wrench to tighten it on the spindle, something I always forget to add when I make them myself.
The endmill holders are available from A2Z CNC