LANCE EN I2C DS1307 Real Time Clock Module for (for Arduino) Tiny RTC 2560 UNO R3 : Amazon.ca: Electronics
Amazon.com: DAOKI 5Pcs RTC I2C Module Arduino I2C RTC DS1307 AT24C32 Real Time Clock Module 24C32 Memory High Precision for AVR ARM PIC SMD Compatible with Arduino with 60 Pin : Electronics
Raspberry Pi RTC Module DS1307 Real Time Clock Module with BAT and Coin Battery for Raspberry Pi
Amazon.com: Tiny RTC I2C - Módulo de memoria 24C32 DS1307 (5 unidades, sin batería) : Electrónica