Countrywide Financial and Wells Fargo accounted for more than one fourth of the total volume of mortgage securities produced during the first quarter of 2006, in a market that still makes room for much smaller institutions to play a role. Countrywide produced $81.84 billion of mortgage securities during the first quarter of this year, giving the company a hefty 16.1 percent share of the market. The company’s MBS production during the first three months of… [One data table included]