Plantastic Plant Products offers several different external auxin/hormone regulators. They can be found for sale online at ecogrow.com

PowerBloom - a concentrated powder mixed and sprayed, which inhibits stem elongation and promotes more lateral branching and bud formation.

SensaSoak - a germination soaking solution to gentically promote feminine plants before the natural expression occurs within the young plant.

SensaSpray - an ethylene compound sprayed on seedlings at the time of sexual determination to encourage feminization and stoutness.