Lewis & Short

sub-sortĭor, tītus, 4, v. a., jurid. t. t., to choose by lot as a substitute, sc. a judge in place of one rejected by the parties: judicem, Cic. Clu. 35, 96.
Absol.: subsortiemur etiam in M. Metelli locum, Cic. Verr. 1, 10, 30.
Part. in pass. sense: si ex lege subsortitus non erat Junius, Cic. Clu. 34, 92.