Private Military Contractors: Lots of them, especially since the Laws and Customs of War in the Eldraeverse recognize mercenaries as legitimate combatants (it should be noted that the Imperial sense of honor takes no issue with fighting for money as long as you stay bought; loyalty to one’s contract is still loyalty, savvy?), and there isn’t any particular rule about them only being able to sell their services to their host polity, or indeed, only to a polity, either.
The grandmother of them all, of course, is the Mega Corp Ultimate Argument Risk Control, ICC, which both supplies its own military and security forces, and brokers the services of other mercenary companies. It can supply everything from local security (down to bouncers), public police services, regular mercenary companies (up to army-sized), privateer starships, naval task forces, and even strategic defense solutions.
But there are plenty of smaller (but still large enough to be effective – see NGO Superpower) mercenary outfits around, especially out in the Expansion Regions. If you need to hire some force, you will have no trouble finding someone to sell it to you.
Oh, yes, and they’re called mercenaries. We don’t do euphemisms.