A new sculpture by one of Maine’s best-known contemporary sculptors has been acquired by the Portland Museum of Art and will be installed Thursday in the museum’s outdoor sculpture garden on High Street. John Bisbee’s “Hearsay” sculpture represents a giant cone made of brightly colored 12-inch spikes or nails. It has been on display in the museum’s Great Hall. Graeme Kennedy, the museum’s spokesman, said the sculpture will be shown permanently in the Joan B.