If you have TOR browser and DarkWeb. This is very much possible. For your security reason no one giving this as suggestion mate. Using TOR upon your own risk only mate. If you want to buy assest under your country taxation limit with the fiat cash.
There you would not get any trouble mate. If you invested on money with the bitcoin for Gold and Silver purchase no one would accept it.
As op shares the various websites acceped BTC. Here below I am sharing the websites accepts the BTC. This would help more I believe.
https://99bitcoins.com/who-accepts-bitcoins-payment-companies-stores-take-bitcoins/