There are no journals devoted exclusively to the cello. However, the following include cello coverage:

American String Teacher  print and online  https://discover.library.unt.edu/catalog/b3713795

Journal of String Research  online only  https://discover.library.unt.edu/?q=%22journal+of+string+research%22&search_field=text

Strad  print and online  https://discover.library.unt.edu/catalog/b3730560

Strings  print and online  https://discover.library.unt.edu/catalog/b3730608