The well known web portal Deeper Blue includes OBAC...

Deeperblue offers deep tank courses. The courses are hosted by Deeper blue and instructors are worldworld famous divers such as Tanya Streeter.

This is what it says:

Qualified FreeDivers

The S.E.T.T facility is ideal for experienced FreeDivers as well. We run a scheme where qualified or experienced FreeDivers can join our instructors in the tank for up to 2 days FreeDiving.

Pre-Requisit

To be able to take advantage of this option you need to have completed one of the following courses:

• DeeperBlue.net Course
• Performance FreeDiving (all levels)
• AIDA FreeDiver (*, ** or ***)
• LearnFreeDiving.com (all levels)
• F.R.E.E (all levels)
• PADI FreeDiver Speciality
• Apnea Academy
• OBAC (Alpha to Omega)
  
  Check out Deeper Blue http://www.deeperblue.net/courses/