It was while I was browsing Forge World for AdMech insignias that I stumbled across the answer.
What about the Iron Hands?
They're loyalist (which is my preference) and they're augmentation-freaks that are similar in many ways to the Mechanicus. What's more, they fought with the Tallarns during the Battle of Tallarn against the Iron Warriors during the Heresy. Close ties with the Mechanicus mean that they'll be plenty of Servitors and Tech Priests running around too.
GW even still sells the old Iron Hands box set.
I think I have a theme. :)