Hungarian Mathematical Olympiad (1964 1997):

Kseniya Garaschuk, "Grade Five Competition from the Leningrad Mathematical Olympiad: 1979–1992 "
English | ISBN: 3030529452 | 2020 | 178 pages | PDF | 2 MB

Jiagu Xu, "Lecture Notes On Mathematical Olympiad Courses: For Senior Section - Volume 2"
English | ISBN: 9814368962 | 2012 | 296 pages | PDF | 22 MB

Yuefeng Feng, "Combinatorial Extremization: In Mathematical Olympiad and Competitions"
English | ISBN: 9814730025 | 2016 | 232 pages | PDF | 44 MB

Kunal Singh, "Problem Primer for the Pre Regional Mathematical Olympiad"
English | 2019 | ISBN: 9386506769 | PDF | pages: 157 | 25.8 mb

A. Gardiner, "The Mathematical Olympiad Handbook: An Introduction to Problem Solving Based on the First 32 British Mathematical Olympiads 1965-1996"
English | 1997 | pages: 252 | ISBN: 0198501056 | PDF | 9,1 mb

Mathematical Olympiad In China (2011-2014): Problems And Solutions (Mathematical Olympiad Series) by Xiong Bin
English | 2018 | ISBN: 9813143746 | 368 Pages | PDF | 4 MB

The Colorado Mathematical Olympiad and Further Explorations: From the Mountains of Colorado to the Peaks of Mathematics By Alexander Soifer (auth.)
2011 | 408 Pages | ISBN: 0387754717 | PDF | 4 MB

Mathematical Olympiad Treasures By Titu Andreescu, Bogdan Enescu
2004 | 241 Pages | ISBN: 0817643052 | DJVU | 4 MB

Bin Xiong, Peng Yee Lee, "Mathematical Olympiad In China (2009-2010): Problems And Solutions"
2013 | ISBN: 9814390216 | 204 pages | EPUB | 7,9 MB

Bin Xiong, "Mathematical Olympiad In China "
English | ISBN: 9814390216 | 2013 | 204 pages | EPUB | 8 MB