This is a flexible duct connector. It consists of a vinyl impregnated fabric pinch rolled into two strips of metal.
It is sold in strip rolls. The strip is cut and formed to make the size you need. Connections are formed on the ends of the sheetmetal to meet the job requirements. Every one is custom.
Contact a sheet metal shop or hvac contractor to have a new one made.
This is one manufacturer of the product.http://www.durodyne.com/ConnectorMetalFab.php