Two Orange County metals supply companies have merged to form a full-line steel and aluminum supply center. Greco Metals Inc., formerly of Garden Grove, and Progressive Steel Supply Inc. merged this spring and have moved into Progressive's expanding Anaheim facility. The new company, Greco-Progressive Inc., forecasts $5-million sales for the 1986 fiscal year. Gordon Edwards, Greco's president, heads the new operation. Greco-Progressive's vice president is Shelley Browns, formerly Progressive's president.