Some subject search terms to try in SOLO
Constitutional courts
Political questions and judicial power
Separation of powers
Judicial ethics
Judicial independence
Judicial review
Judicial process
Most consitutional courts have their own website with accessible databases of decisions. Some also provide (unofficial) English translations of their leading cases.
In addition, the Council of Europe's Venice Commission monitors constitutional developments world-wide (not just members of the CoE) and makes results available free online: