silkroad had made sales over 9.5Million BTC and revenue of around 600,00 BTC,
are this 9.5 million BTC are flagged by US government? is it safe to buy bitcoins from these 9.5million btc (maybe from 9.5million flagged btc)
The estimates you mentioned are very exaggerated, and the closest to accuracy is that the trading volume was 9.5 million, i.e. the total transactions processed by Silkroad, and 9.5 million dollars, not Bitcoin, but it is impossible for their wallet to contain more than a million dollars.
In general, the story is very old, and most of the responses here are for people who created accounts after the year 2014, so we will not know what was happening at that time, and all we can tell you is what everyone can find from searching in Google or news sites.
This story no longer resonates and I rarely find analytics linking bitcoin to the dark web or drug trafficking, or at least not as much as I did when I joined the forum in 2017.