You could have a look here.
https://www.susans.org/forums/index.php/topic,167887.msg1661891.html#msg1661891Brewers yeast is a supplement that should be readily available. In your country its called biolabor bierhefe (tip from an aquaintant).
Its available with or without zinc.
Look at the link above if you take meds for depression or have diabetes.
It was listed in wikipedia as for hair growth. Some people have reported over the half more in a few months.
You could take it for a few weeks... and you can look it up on amazon, there are ratings of other people there...
Is the rest of your nutrition healthy ?
Not too much sugar or high sugar drinks... enough fruits and vegetables... not too many artificial components...
maybe no artificial sweeteners, rather natural ones or brown sugar which is less refined...
Nutrition can make a difference... and imo not washing hair too often, or with an organic product, so not to use too many chemical components.
hugs