Your search for "asa5516-bracket" revealed the following:
NetworkTigers ASA5516-BRACKET Rack Mount Bracket Kit for Cisco ASA 5516 Series
SKU: NSB-8444
Condition: New
Shipping: Overnight Options
Warranty: 365 days
$ 15.95
• 50 in stock
Call if you need more
Cisco ASA5516-BRACKET ASA 5516-X Rack Mount Bracket Kit
SKU: NSH-8763
Condition: Seller refurbished
Shipping: Overnight Options
Warranty: 365 days