I see this used both ways in advertising materials, but am not sure which is correct. I could not find any reference to this when searching the internet.
Both of and on are used when speaking of such courts. of casts its object as something to which one can belong as a member belongs. on casts is object as something which affords a position.
He is a member of the committee.
He has a position on the committee.
He is a member of the court.
He has a seat on the court.
He has been a judge on the Court of Common Pleas for ten years now.
He has been a judge of the Court of Common Pleas for ten years now.
Here are some examples in the wild:
Lycoming county is within the eighth judicial district; and thus, it appears that the affidavit was sworn before a judge of the court of common pleas of Lycoming county.
And later, after Judge Onion became a Judge on the Court of Criminal Appeals, his twin brother, James, was also elected to serve as judge on the same district district court where their father had served.