Hi Markus; Miami isn't a strong market for acoustic guitars ... stronger for semi/solid body guitars. It also doesn't have older, long-standing music stores ... only 'Big Box' retailers whose inventories of Guilds tend to be skimpy:
Sam Ash
11421 NW 12th Street
Miami, FL 33172
Phone: 786-331-9688
They also have stores in northern Dade Cty in Miami Lakes and another in Margate, west of Ft Lauderdale.
Guitar Center
7736 N. Kendall Dr.
Miami, Florida 33156
Phone: 305-271-2600
Link to Sam Ash
Store Locator and to Miami-area
Guitar Center
CJ