Russia.
Or OPEC.
Or the EU.
Or any of a number of global interests.
Russia - experiencing extreme economic problems with devaluation of the ruble;
OPEC - the steep decline in oil revenues has resulted in severe economic stress;
EU - they might buy some, but they have their own problems and are trying to sell their own debt.
If yyou don't believe me, research it. We're in a period of deflation and the old ponzi scheme of debt is beginning to crumble. The Fed can continue for a while, but eventually something has to give.