Were are did the mercenaries go?

I played my friend against his orks and began to wonder about their background story. I went on to lexicanum 40k and began reading about orks and came across reading that some ork blood axes work as mercenaries like the kroot to other alien races even though it's un-orky. I started to look for rules and found none and remembered that kroot had rules for an all kroot army in the old chapter approved books but are know obsolete. I began to think if there were any human mercenaries like in the Star Wars universe made famous by Han Solo and Boba Fett and couln"t find any. I usually find that humans are either for the imperium or against it and not in between; mind you not I am talking about mercenaries and not pirates like Dark Eldar. I also just finished reading the novel Flesh and Iron by Henry Zou :BOOK SPOILER ALERT: and was intrigued that the main character began working for a chaos space marine somewhat as a mercenary and was respected as such but did not turn over to chaos as do many people believe when one is affiliated with chaos. So I decide to turn my army to a mercenary army because I tend to fight alot of Imperial armies very loyal to the emporor such as Imperial Fists, Grey Knights and Space Wolves.

To represent this in my army I am going to limit myself on vehicle selections especially heavy support as the Elysian drop troops do because of the lack of Imperial support mercenaries recieve and fast manuevering they have to do to avoid being captured and destroyed from EVERYONE in the galaxy they are working against or created bad blood with. I am also going to include models from diferrent xeno races such as Orks and Tau to show that my mercenary group refill their ranks to replace losses that occur on different missions and encounters. I will began repainting some of my figures to represent this change. If you ask why not Nids and necrons, well I seen conversions were Nids can be controled with remote controls in their heads and Necrons we can say were reprogrammed. This idea is just for regular home games. I don't think this is turney legal because usually you must use only your army models unless they are converted to resemble your army some way.

Let me know what you guys think of this because I like to read more on mercenaries in 40k other than Tau allies.