For development agencies, search directly for their vacancy pages. For instance you can see how to go about accessing COMESA vacancies, United Nations jobs, USAID hiring for foreign positions,UNIDOemployment, and so on.
A word of caution though, beware of fraudsters who advertise non-existent jobs. Always check on your targeted organization before applying. Disclaimer: BUCADEF is in no way connected with the above advertised positions. So do your own due diligence and pick out what you are sure of.
And if all this doesn't help yet, especially for youths, think seriously of improving your skills in a specific area instead of just relying on head knowledge. It is frequently not lack of jobs, but lack of skills to take on the available juicy jobs. We hope to include some kind of skills improvement modules on this website at a later stage.