Try Catamaran Company or Barecat.com
I have done 15 bareboat charters in the USVI/BVI and have chartered cats 3 times, 2 times from The Catamaran Company (Privilege 43 and 48) and once from a company now out of business (Lagoon 41). The Catamaran Company is excellent, but expensive. Also check out www.barecat.com. Keep in mind, contact me at robertclasalle@cs.com if you might be interested in chartering my brand new, fully loaded Hunter 450 center cockpit sloop based in Miami Beach, easily accessible to the Florida Keys and the Bahamas.