About the Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter - Apple Support
Original Official for Apple Thunderbolt 3 USB-C to Thunderbolt 2 Adapter Converter Cable MMEL2 A1790 White - AliExpress
StarTech.com TBT3TBTADAP Thunderbolt 3 to Thunderbolt 2 Adapter - Backward Compatible - USB C to Mini DisplayPort - USB-C to Thunderbolt 2 - Newegg.com
Amazon.com: StarTech.com Thunderbolt 3 to Thunderbolt 2 Adapter (Non-Reversible) - TB3 Laptop to TB2 (20Gbps) or TB1 (10Gbps) Devices / Displays - Black - Windows/Mac (TBT3TBTADAP) : Electronics