Your search for "1000SFP31B20L" revealed the following:
Champion 1000SFP31B20L 1 Gigabit 1310nm SMF Single Strand Transceiver SFP
SKU: NSB-9034
Condition: Seller refurbished
Shipping: Overnight Options
Warranty: 365 days
NEW Champion 1000SFP31B20L 1GB 1310nm SMF Single Strand SFP Transceiver
SKU: NSN-0823
Condition: New
Shipping: Overnight Options
Warranty: 365 days