There seems to be a typing mistake. The embouchure should have diameter of 2.8-3.2 centimeters, not millimeters. Perhaps that can be done DIY from an PVC pipe with an hot air gun or a gas burner to soften and shape the end.
"Participants received a standardised acrylic plastic didgeridoo that was developed by the instructor in collaboration with Creacryl GmbH (Ebmatingen, Zurich, Switzerland, and costs €80 (£43; $94), fig 1). The didgeridoo is 130 cm long with a diameter of 4 cm and an elliptical embouchure with a diameter of 2.8-3.2 mm. Acrylic didgeridoos are easier for beginners to learn on than conventional wooden didgeridoos."
"Participants received a standardised acrylic plastic didgeridoo that was developed by the instructor in collaboration with Creacryl GmbH (Ebmatingen, Zurich, Switzerland, and costs €80 (£43; $94), fig 1). The didgeridoo is 130 cm long with a diameter of 4 cm and an elliptical embouchure with a diameter of 2.8-3.2 mm. Acrylic didgeridoos are easier for beginners to learn on than conventional wooden didgeridoos."