Where can you buy hydrquinone 6

Google " 6% hydroquinone". Loads of info. Since we have no idea where you are located, we can't help much.

Actually you will not find 6% hydroquinone by itself, but as a small element in other compounds. It is a chemical that is used, at least in America by prescription to help with freckles, spots and small areas of discolor on the skin.
While still legal by prescription in America, it has been banned in many countries.

It has still be allowed in America due to the fact is is always mixed in other products, thus the actual percentage being used is very small.