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