A Hudson Valley Showcase of two dozen of the region's buildings and sites is scheduled for September 25 from 8 to 9:30 a.m., at 440 Mamaroneck Ave.  Open to area commercial real estate brokers and corporate end users, the event includes breakfast, a property tour and networking with top real estate owners and brokers in the nine-county region. "In 90 minutes before going to work in the morning, brokers can really get up to speed on commercial real estate in the Hudson Valley from New York City to Albany," said Anthony Campagiorni, president and CEO of the Hudson Valley Economic Development Corp., which is hosting the event.   The showcase will feature a tour of 440 Mamaroneck Ave., which has been undergoing a renovation by its new owner, RPW Group, to transform the 245,000 s/f building into a multi-tenant property.