I live in DC, and I can have access to key people. I am clear what is my goal for this next decade. I want to build and maintain a professional network in DC and in my original country. I don't want to just knock doors. I want to strategically know the people to reach, what is the WIFIIT for each network group, and how to maintain the network.
So it sounds like your question is really two questions:
1.) How do I find the right people to invite to my network and build relationships with?
2.) Once I define who those people are, how do I go about building that relationship, or network, and how do I sustain it over time?
As for the first question, I would agree with what David said, Meet Up's can be a good place to start. Doing LinkedIn searched with a "geo-filter" for the DC area could be effective as well.
Meet Up's might be a good way to initially meet some of the stakeholders you're hoping to make contact with, but building a strong foundation for a relationship, and maintaining it may be a little more challenging. Not all Meet Up's are structured the same way, some are effectively facilitated, and some are not.
It could be most effective for you to create your own "community building" or "networking" Meet Up that's centered around your own specific idea, issue, or industry, and then go to other related Meet Up's in order to invite people to your own Meet Up that you have more control over.
What I mean by "control" is you can have more control over the "networking" or "community building" frameworks to accomplish those very things. Examples: What is the physical structure of where the Meet Up is taking place? Is it a place that everyone is comfortable and is conducive to community building? What dialogue strategies or protocols could be used to ensure that all parties are heard, understood, and valued to ensure that everyone wants to come back to another Meet Up? Maybe it makes more sense to hire a 3rd party facilitator to help manage this process?
In closing, there are lots of things to consider, let me know if you want to book a call with me and we can take a deeper dive.