Flag of Orkhon Aimag in Mongolia.
Official mention and example: http://www.ith-orhon.mn/нутаг-дэвсгэр
Shows a flag of unclear proportions. The scanned description seems to describe a different flag than this, but mentions dimensions of "1x2 meters". This (probably older) flag included elements similar to the current COA (meanders of the orkhon river, a lion sculpture, the chandmani, and the written text "Erdenet").

Real usage photos: http://www.ugluu.mn/200720.html Clearly show 1:2 size ratio (the usual ratio in Mongolia)
Own work Based on Vexilla Mundi: http://www.vexilla-mundi.com/mongolia_divisions.html
Dalakop