First, it needs to operate under some sort of a legal framework. So it would be established by some sort of treaty countries could ratify. Realistically we are probably talking about EU, Japan and few other countries that use economic and political pressure to make countries in Latin America, Africa and Asia ratify it.
Countries such as the US, Russia, China and Israel would reject idea outright. The idea of outside force enforcing human rights on them would be politically too corrosive to touch. The Arab countries would also avoid this because they have issues with the definition of human rights. They might still cooperate and support the organization unofficially on a case by case basis.
In fact the above might be a good explanation of why it must be held separate from the UN and other organizations the above groups are members of. They'd simply have to oppose such organization for reasons of internal politics and nothing would get done.
So where would the organization come from? Well, there would have to be some sort of a crisis where human rights were majorly violated but direct government intervention would have been a pain. This is fairly realistic in that major powers do not really like other major powers having large occupation forces in other countries. And tax payers do not like paying for such armies. Or reading about the inevitable casualties.
But the crisis was urgent so instead a it was decided to create a military contractor to do the job with mercenaries and authorize them to do the job of overthrowing the government with oversight, funding and volunteers from participating governments.
The result is the military contractor occupying the target country. And its resources.
If we then assume that the operation was a great success, ie the problem was solved and none of the dirt got attached to politicians, and that another crisis happened before the military force was not disbanded, it would be only natural to use the same solution for that crisis as well.
And to fund it with the resources of the first target.
Basically the new civilian government established for target nations would give the contractor a cut of the profits of the their resources to pay for maintaining security and overseeing human rights and good governance.
In practice, the contractor would hold the resources independent of the host nation and provide funding for those civilian projects it approves of. And the host nation would not have any military force or money to fund one to challenge the contractor.
This would be really neo-colonialism but with it only happening to countries where people have very good reasons to not trust their own government with either soldiers or money, it might genuinely be the lesser evil. It would certainly be possible to sell it as such to people on another continent getting all their information about it from your slick PR campaign.
So the answer to your question would be: oil, gold, diamonds, copper and other mineral resources.
Since the contractor would need significant areas of land to use as base of operations and those areas would be outside the jurisdiction of the host country, these "company districts" would quickly acquire significant population and economy. So tax income from that would also become a source of income as the economies recover from the initial crisis.
Additionally, the contractor would also invest some of the money it gets directly to "host nations" to "support economic recovery". It would make profit from those investments.