Hi, I too collect in a Supreme Global to 1976 though mine is built from a 1956 edition and all the annual supplements. With the same problem.
I have the one sided PRC pages sold by Amos with stamps up to 1972, they are in 72 sheets. Everything is the same as you would get with the double sided ones except there are twice as many pages. And spaces for Souvenier Sheets which are probably deleted from the double sided ones.
Minkus at one time did have a double sided set of China pages but they were sold separately from the Minkus Supreme. And it seems like not a lot of people bought them. I have only seen these once. I was lucky to get a dealer friend to sell me the 1972-83 pages from an old collection since they were empty. He kept the older part that had stamps mounted.
You didn't mention it but Mongolia is also in the same category. There was a printing of Mongolia pages in double sided format that were not part of the Supreme albums but separate. I was able to find a used copy of these pages on eBay
Also at the end Minkus gave up on including Trucial States in the Supreme Supplements and sold them separately.
The following was printed on the Letter from the Publisher sheet for the 1973 Global supplement:
Collectors interested in certain areas are advised to use the special Supplements now available from Minkus Publications: Mainland China, Mongolia and Trucial States.
I also would be curious about whether Minkus ever printed pages for North Vietnam, North Korea or Cuba, but since their original policy was to abide by the embargos, we would only be likely to see Vietnam published post-1995.