It would be great to have original factory documentation and government records from the 1950s to 1980s from the PRC. The motivation for building their own weapons manufacturing capability, the transition to geographically distributing that small arms manufacturing capability, the production numbers and locations of all the different arsenals, etc. A team of Mandarin speakers to translate it for us would also be helpful. Of course, emergence of that type of source material is extremely unlikely to happen with the current government and I think would remain unlikely even if a completely reformed, non-authoritarian, relatively open government were to succeed the current one. Regardless, if the information became available, it would have to be read with a critical eye, mindful of the context of a society where the party line was the only acceptable line (especially in Mao's era) and much of the explanations of decisions and history would likely have lapses in veracity typical of that unquestioning political culture.
I'd say the same applies for Russia, a country seemingly doomed to repeatedly slipping into an authoritarian system regardless of economic or political ideology. Yugoslavia likely lost that data in the chaos and bombing of Belgrade and surrounding areas (like Kragujevac). I suspect the data may also be lost for Albania, Romania, and the former East Germany due to the chaos at the transition from a closed to open society (and subsequent crises in the case of destitute Albania). Certainly no documentation on SKS production or history has surfaced, or been uncovered that I'm aware of. Perhaps it's laying in a forgotten warehouse somewhere and a historian will discover it someday. North Korea is in the same secretive government scenario as China, only 10 times more so
I think some of the reasoning behind why possibly no production records or source material exist or have been found.. look at the Cold War leadership from the 1950s to 1980s.
Russia, you had Stalin to start out with.. a ruthless hardcore leader who would purge his own military ranks, two short term leaders followed, then Khrushchev.....Cuban missile crisis ring a bell...then there is Brezhnev..
In Albania you had Enver Hoxha.... this dude had secret police who wiped people, families and towns out of existence, a Stalin fanatic and follower till one or the other started a pissing match, then he snuggled up with Mao, Hoxha personally drove and pounded that little nation into the ground.
China had Mao.... No way anyone really knows all what he did....he supported North Korea, the NVA, killed who knows how many in the name of Communism.
North Korea.. they need no explanation!
In Romania you have the original Commie leader Gheorghe Gheorghiu-Dej who wasn't too bad, maybe he died before he got wound up, but he was followed by Nicolae Ceaușescu....this is where Romania went south, he was a communist wack job who again, killed his own people, in the many of thousands to support their cause..... soldiers finally killed him and his wife.....then in a weird twist, Romania did away with capital punishment.
Then in Yugoslavia you had Josip Broz Tito, yet another fanatical communist...he didn't really get along with Russia.. he really was not quite as bad as some of the above leaders, he would deal with the US and other nations in some ways. When he finally died, the nation of Yugoslavia imploded and blew into little pieces.
I would imagine many of those nations have tried to erase that past and move on, it would be much like trying to find Nazi memorabilia in Germany, it just ain't gonna happen.. if there are records of any production...
Russia to me would be a likely candidate, but like anything, why keep records for almost 70 year old surplus stuff you no longer even have or would even share.. what is the benefit??
The rest of those nations were ruled by what amounts to a...... psychotic, genocidal, serial killer with military access, I would imagine most all documents and any records were possibly destroyed to prevent in depth investigations and charges later down the road....in today's world the truth hurts.. especially economically.
So...that leaves people who were there, hands on, on the production floor, who are now in their prime old golden years with foggy, scared memories of atrocities, horrors and days gone by... The odds of them ever speaking....very slim.