Here you can find a notation sheet of Sandy River Belle for mandocello.
It is in the key of G.
For a sound example played on a Weber mandocello, see in the video section.
Here you can find a notation sheet of Padraig O’Keeffe’s Hornpipe for mandocello.
By the way, it is the melody part played by the 1924 Gibson K-4 in the video section (duet with 1924 Gibson K1 mandocello and duet with Collings OM guitar).