DaVita to Buy Gambro Unit for \$3 Billion  PHILADELPHIA/STOCKHOLM (Reuters) - DaVita Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=DVA.N target=/stocks/quickinfo/fullquote"&gt;DVA.N&lt;/A&gt; is  close to an agreement to acquire the dialysis operations of  Sweden's Gambro AB for about \$3 billion in a deal that would  create the No. 1 U.S. provider of dialysis services, a source  familiar with the situation said on Monday.