Music for Two (or more) Cellos
The webpage johnstone-music.com has a huge selection of fine transcriptions for all sizes of cello ensembles, from cello duos to ensembles with 12 different voices. Clicking on the highlighted link will take you to the website’s home page. When you put the cursor on the “Sheet Music” tab in the top menu, you can select the size of your group and then choose from a selection of over 1000 pieces for the diverse combinations.
Be aware that the number of separate cello voices does not limit the maximum size of the group. For example, while these pieces of music normally have two, three or more different individual voices, they can in fact be played by larger groups, simply by doubling the voices.