By Dave Williams Staff Writer dave.williams@gwinnettdailypost.com DULUTH - U.S. Rep. John Linder has said for years that only a groundswell among the American people will convince Congress to scrap the Internal Revenue Service and replace it with a national sales tax. Wednesday night's rally at a jammed Gwinnett Convention Center in support of Linder's FairTax bill looked a lot like the popular uprising the Duluth Republican has envisioned since he introduced what has become his signature legislation in 1999. "The grass roots are working,'' said Joseph Gullett of Norcross, motioning to more than 100 people gathered outside the convention center...