Where can I find old (historical) FIR map? I'm doing a research with FIR Ho Chi Minh (formerly named FIR Saigon).

I've read a document which said:


During the Fall of Saigon, ICAO, in 28th of April 1975, had divided FIR Saigon into 3 AOR: Bangkok, Singapore and Hongkong, then they gave these AOR to the corresponded FIR.
In the 7th of December, 1994, ICAO sent AOR Bangkok and AOR Singapore back to FIR Ho-Chi-Minh.
In the 1st of November, 2001, ICAO gave part of AOR Hongkong to FIR Ho-Chi-Minh, and created AOR Sanya from the remained part of AOR Hongkong.
In the 8th of June, 2006, ICAO changed AOR Sanya to FIR Sanya


I managed to search those old FIR maps in the internet but no luck for me.

Hence, I would like to find out all historical FIR maps to make a comparison.

If it is impossible to find all FIR maps, old FIR maps of South East Asia FIR is greatly appreciated.
The best I can find is a ATC radar screen used in a dated report (appears to be a report by the Hong Kong Civil Aviation Department in 2000). It shows the FIR regions and waypoints of near Hong Kong, Hainan island and Vietnam:



Here is a dated enroute chart of Hong Kong in 1996. I'm not sure if the waypoint names will be useful for your further search:




How I end up with these: for the first one I used keyword "Sanya AOR". Given the dates you stated in the question, Kai Tak airport was still operational during that time. So I searched for charts of Kai Tak. A full set of charts of the airport would contain an "enroute chart" which lists waypoints. Search engine is Bing.