Wolf Tooth Components - Some I-SPEC II shifters are designed to only attach to an I-SPEC II brake. So, if you had an I-SPEC II shifter but no compatible brake, you were
KCNC I-Spec II Shifter Clamp - Fair Wheel Bikes
Shimano Deore XT M8000 Clamp Band I-SPEC II Shifter - - Capitol Cyclery
KCNC Lever Clamp for Shimano XTR/XT M-9000/M8000 I-Spec II Shifters (1 pair)
Problem Solvers MisMatch Adaptor 1.2 - I-Spec II Brake to SRAM Shifter - Fanatik Bike Co.