If Christians really believed that getting the Gospel into all the world was as important as it really is...
North Korea is the most difficult country for missionaries to gain entry. The border with South Korea is a demilitarized zone and almost no one gets through without being shot or blown up by mines. Their northern border with China is difficult to pass through as well. I don't know how possible sea access is. There are some ways the Gospel is getting in, but I think it's safe to assume missionaries are needed in that country.
If Christians really believed that getting the Gospel into all the world was as important as it really is, we would brainstorm and come up with every possible way to get the Gospel in to unreached places. Once we came up with those ideas, if they were promising, we would spend the necessary time, effort, and money on those ideas to get the Gospel out there. Now, in most places of the world, it's pretty straight forward--send native missionaries, do radio broadcasts, internet evangelism, Jesus Film, literature distribution, etc. North Korea is different though. It requires creativity.
If you skydive with a wingsuit from 30,000 feet at the north end of South Korea, you could glide 5 miles into North Korea. You could go with a big bag full of literature to distribute, hide out in the woods, make contacts with people whenever you can, and pray that you don't get caught. The point here is that if we truly believe Jesus saves, we would see hundreds of believers volunteering to do something this crazy.
If you are serious about getting practical, I have better ideas than this. If you want to know about them, email me.
Never heard of wingsuits before? Check out this video.
(If any North Korean official reads this, you should know that the goal of Christians is not to undermine or overthrow any government. Our goal is to tell people how they can get to Heaven. We want to share Jesus' teachings, and people will learn how to better love one another, and be honest, good citizens.)