Mayor Michael R. Bloomberg of New York and the billionaire philanthropist Eli Broad have each donated hundreds of thousands of dollars. The National Rifle Association is buying political advertisements. New York’s junior senator sent a fund raising e mail. And the election has attracted news coverage from as far away as Sweden.All this over a homegrown campaign to oust two Democratic state senators who provided crucial support for a package of strict new state gun control laws. As the recall elections the first of their kind in Colorado’s history draw closer, the race has swelled from a local scuffle into a proxy battle in the nation’s wrenching fight over gun control.