Mega Sudoku 16x16 Ser.: Mega Sudoku 16x16 - 200 Very Hard Puzzles Vol. 4 by Liam Parker (2019, Trade Paperback) for sale online | eBay
Sudoku - 16x16 Puzzles
Hard 16x16 Alphabet Sudoku Ser.: 16x16 Super Sudoku : Hard 16x16 Full-Page Alphabet Sudoku, Vol. 3 by Thomas Schreier (2017, Trade Paperback) for sale online | eBay
Whew, I finally completed my first 16x16 sudoku : r/sudoku