IBA is costly and available in Chemical labs. Prepare 100 ppm (parts per million) IBA by dissolving 100 milli gram IBA in 100 liters water ( or 1 mg in 1 lit by accurate pippette ie scientific equipment). Also prepare 200, 400, 600,1000 and 2000 ppm solutions. (with the help of a chemist as far as possible to ensure accuracy).
Then dip 3 cuttings each in separate vessels filled with above solutions. Then wait for a few days to watch. If more rooting happens in any of the above combination, select that. Or continue experiment with other combinations like 1500, 2000, 2500, 4000 etc. If more roots come in any say 500 ppm then you can get more accurate results if done again with 400, 500, 600 ppm separately to catch right ppm.