Scouting SoHo Designer Samuel Botero Heads Downtown for a Distinctive Mix of Old and New Text by Wendy Moonan Photography by Theo Westenberger Todd Merrill is a dealer of 20th-century modern furnishings who has just moved to Bleecker Street.  "He has a keen eye for pieces with style and quality and doesn't make you break into Fort Knox to pay for them," Botero says.  If you love it, buy it; chances are it will be gone quickly." Merrill is a third-generation dealer.  "I began   working in my grandparents' shop, selling Americana before I was 12," he recalls.  Five years ago he decided to open his own place, specializing in American designers of the 1920's to the 1980's, such as Milo Baughman, Vladimir Kagan, Karl Springer and James Mont.  "I had the feeling midcentury was about to explode because the quality is so good," he says. "There's still a lot of research to do, but there are wonderful things out there to be discovered.  The whole 20th-century thing used to be a secondary market.  Now it's bringing in a huge new customer base."	Todd Merrill Above: A 1968 Hand chair by Pedro Friedeberg is among the mid-century discoveries Todd Merrill, left, features at his shop. Botero leans on a Hugh Action bench.