That is NOT the way it is being done. There is a thriving smuggling trade between North Korea and China.
This is mediated by North Koreans who are desperate enough to risk the penalties for being caught. Stuff stolen from the North Korean government, especially the army (not weapons), is being exchanged for food, clothing, and radios.
In addition, there are anti-communist groups that use small balloons with parachutes to send the radios over the border. The balloons are launched when winds are favorable. They rise until the pressure is so low that they burst, releasing the radios on parachutes, to be found by the North Korean population.
