MEXICO CITY'S ZONA ROSA, THE HIGH-RENT ZONE, IS FILLED WITH U.S. BUSINESSMEN THESE DAYS, ACCORDING TO RICHARD MARTIN (404)-980-2000 OF THE UNIVERSITY OF GEORGIA'S SMALL BUSINESS DEVELOPMENT CENTER IN ATLANTA, WHO RECENTLY RETURNED FROM A TRIP WHERE HE WAS STUDYING DISTRIBUTION SYSTEMS IN MEXICO FOR TWO GEORGIA MANUFACTURERS. WHETHER OR NOT GEORGIA MANUFACTURERS CAN FIND IMMEDIATE SALES FOR THEIR PRODUCTS, THEY NEED TO ESTABLISH RELATIONSHIPS NOW WITH THE KEY DISTRIBUTORS BEFORE THEIR COMPETITORS DO, HE SAID.