Fabian -
Where do you live? Do you know what the requirements are in your country, and with your regional health insurance companies, to be covered through insurance? Do you need specific referals from doctors?
The teachers i know who are able to receive payments in the US for teaching yoga to private students have made arrangements to provide these services through Physician’s offices, or through hospital programs like Dean Ornish’s heart health program. You would only be able to get those referrals for patient’s who had the insurance, and it would probably be better if you went to a therapy training program. A good one is more than 500 hours.
If you are looking for ashtanga yoga training in the style of Pattabhi Jois, you would probably want to look around Mysore for teachers who offer a a similar training and offer 500 hour certifications. The actual school of Jois does not offer 500 hour certificates, only teaching authorization, which is based on personal performance and may take years. If you are look for ashtanga yoga training as in all eight limbs of study, then I suggest searching through your country’s yoga-teacher registry to see which schools they list for INdia. If you are in the US/UK, check for schools registered under the respective Yoga Alliance or British Wheel of Yoga. I’m not sure what the EU alliance is.
There are MANY schools, in India. They all teach something different. What worked the best for me was finding teachers that I liked, and then following the path to where they studied and going there myself.