Tooling, parts, and accessories for bench top machinists - LittleMachineShop.com
located here in Pasadena, CA. I know the owner and can vouch for their operation - very professional and excellent custormer service. (No, I have no business connection with them.)
On a different note. Rather than adapting a Dremel chuck, why not get some conventional pin vises, e.g....
and chuck those in the Unimat 4jaw? Even if their precision is less than perfect, the work can always be made to run true with the 4jaw. That arrangement should give you adequate angular access to the part.