Dfrobot Mega I/o Multi - Expansion Shield Support 4 Shields Compatible With Arduino Mega1280/2560/adk For 3d Printing Robot Etc. - Demo Board - AliExpress
Amazon.com: Velleman VMA05 I/O Shield for Arduino, 1 Grade to 12 Grade, 2.75" L x 2.16" W x 1.18" H : Electronics
Amazon.com: Teyleten Robot Nano IO Expansion Shield Sensor Module for Arduino UNO R3 Nano 3pcs : Electronics
Amazon.com: CQRobot Ocean: MCP23017 IO Expansion Board Compatible with Raspberry Pi/Micro:bit/Arduino/STM32 Motherboard. I2C Interface, Expands 16 I/O Pins, Up to 8 Expansion Boards Can be Used Simultaneously. : Electronics
Amazon.com: 10Gtek Nano I/O Expansion Multi-Purpose Extension Sensor Shield Module for Arduino UNO R1 R3 Nano red, Pack of 2 : Electronics