Iīll order it for you in the factory. 100 hard, 100 normal. 40x50 cm

Unfortunately the paper makers never have paper sitting around or in stock.
Thatīs the part of the probelm. If they were keeping a stock everybody could buy from it and overall quantites would be reasonable.
Rather they turn everyone down and always ask for complete factory runs.
They need eneourmoue quantites and then donīt want to store it.
A papermill only makes money if it is constantly producing paper day and night. Even offering them more money does not help.
The base is cheap compared to the price of the coated paper but only if made in hundreds of tonns.

BUT the new base will not be 180 (standard double weight) but 280. So it will still be heavier than most other papers.
I hope your work can be continued on 280g without too many problems.