Universal ATMEL AVR ISP programmer from heilingch on Tindie
Adafruit 6-pin AVR ISP Breadboard Adapter Mini Kit : ID 1465 : $0.95 : Adafruit Industries, Unique & fun DIY electronics and kits
Batsocks - AVR ISP Header Pinouts
AVR-ISP-MK2 - Open Source Hardware Board
Kanda - Guide to AVR ISP Circuit Schematics
Amazon.com: for ATMEL 51 AVR USB ISP ASP Microcontroller Programmer Downloader with Cable + 10Pin to 6Pin Adapter Board for Ender 3 or Ender 3 Pro Geekstory : Electronics