Pictures are from: http://www.lostbulgaria.com/ And others courtesy of Klaus Ahlf and Nick Stanev
Vendors:
A-H Stuff
http://www.ladownica.pl/galeria.html
https://www.militarie-repliky.cz/en/rakousko-uhersko.html
https://www.kukreplika.cz/en/repliky/rakousko-uhersko/
Russian
http://voin.zp.ua/index.php?route=product/category&path=68_87
http://military-ussr.in.ua/en/home/uniforms-of-the-russian-imperial-army
https://schusters.ru/en/russia-1914-1917/?v=7516fd43adaa
https://www.voenspec.ru/catalog/7036/
https://leibstandart.com/reenact/2859/
German
https://nestof.pl/en/menu/great-war-1914-1918/germany-1918-274.html
http://www.gavinmilitaria.com/index.php?main_page=index&cPath=115_116
https://schusters.ru/en/germany-1914-1918/?v=7516fd43adaa