I understand SDI has been offering a solo diver course 1999, so it's a more established course among SDI instructors.
If you intend to go solo, maybe try looking for a SDI instructor?
A quick search on the SDI website
lists the following agencies:
- Planet Scuba
- Diving Solutions (Asia)
- Bolsen Marine Systems
- Deep Fathom
- The Dive Company
- Red Scuba
- Free Bubbles Scuba Studio
Disclaimer - I'm not affiliated to any of these agencies..