There's DOUBLE EXCLAMATION MARK[0] and also DOUBLE QUESTION MARK[1] if those will do.

[0] https://www.fileformat.info/info/unicode/char/203c/index.htm

[1] https://www.fileformat.info/info/unicode/char/2047/index.htm

Besides interrobang, Unicode includes all 4 possible sequences of 2 "?" and "!".

  203C;DOUBLE EXCLAMATION MARK;Po;0;ON;<compat> 0021 0021;;;;N;;;;;
  203D;INTERROBANG;Po;0;ON;;;;;N;;;;;
  2047;DOUBLE QUESTION MARK;Po;0;ON;<compat> 003F 003F;;;;N;;;;;
  2048;QUESTION EXCLAMATION MARK;Po;0;ON;<compat> 003F 0021;;;;N;;;;;
  2049;EXCLAMATION QUESTION MARK;Po;0;ON;<compat> 0021 003F;;;;N;;;;;