From The History of Standard ML, footnote 12:
Polymorphism -- The ML/LCF/Hope Newsletter was self published by Cardelli and MacQueen at Bell Laboratories and distributed by physical mail to interested parties. Electronic copies are available at either http://lucacardelli.name/indexPapers.html or http://sml-family.org/polymorphism.
The second link results in 404.
I do not see those papers uploaded in this github repo. Perhaps, the newsletters are just yet to be posted here?