How to make Home made tonic water

I tried to make my own tonic water.
Checking some website (here , here and here ) , cinchona is important for tonic’s specific bitter taste.
But cinchona is prohibited selling in Japan. so I can’t use it. I should look for alternative choice in my home.

Ingredient
1l. water
1 lime
1 Lemon
1 orange
2 stalks of chopped lemongrassAllspice berries
Cardamon
Angostura Bitters
3 tbsp. citric acid
2c. sugar
1 tbsp salt

Cut and squeeze all fruits and spices , boiled them about 20 min.

Then filtered out by chemex .

Effected by allspice , cardamon and Angostura bitters, the taste is bitter .

Added 2 spoons of it in gin and soda , It would be a home made gin tonic.