The Rainmakers today are Jeff Porter (from left), Bob Walkenhorst, Pat Tomek and Rich Ruth. The band will spend two weeks touring in Norway and will play a May 14 show at Knuckleheads. The band’s new album, “25 On,” will be officially released Monday, March 14. It is available now at Village Records. In a booth at the RecordBar, about an hour before one of his weekly gigs, Bob Walkenhorst is talking about anniversaries. This is a year of a few, starting with his band the Rainmakers. Twenty-five years ago they released their first and most successful album, “The Rainmakers,”…