Aluminum Derailleur Bolt (where to find)

[Lelandjt]

You know the bolt that mounts the derailleur to the hanger? You know how it has a long unthreaded shoulder where it passes through the derailleur? Well I need a short one (12-20mm) with a very short unthreaded section (<6mm or none at all) because I want to mount a singlespeed chain tensioner that has a fairly thin mounting arm. This thing came with no mounting bolt! So I'm looking for an aluminum M10x1.0 15ish mm long, ideally with a button head so it has a large shoulder to provide radial hold on the the tensioner.

EDIT: Nevermind, I remembered that shadow derailleurs use exactly the bolt I need.