At my alma mater (Indiana University of Pennsylvania), our tuba professor, Dr. Zachary Collins, started a project called bass clef duets. Although this is not exactly a post that is international, it can be assumed that his duets reach an international audience of brass duos.
For any low-brass player, I think these are a good find and the best part is that these are free!
There's even a Facebook page for this project!
Below are two duets Dr. Collins wrote this year: