Hi Andre, I have a few thoughts that may (or may not) be useful:
First, have you tried the PEI university archives? They have newspaper and other records that I've found useful: http://islandarchives.ca/
Second, I wonder about church archives. Depending on the religion of your branch of Cains, there may be records elsewhere. For example, I found useful information about one of my PEI Bradshaw ancestors in the Baptist Archives in Wolfville, Nova Scotia.
Third, I have also found useful information about PEI ancestors in the NB and NS archives. There was a lot of back and forth among the early maritime families.
Last thought, if you scroll down on the two PARO pages that you found referring to the PEI Supreme court, there is a line at the very bottom that says "Contact Us to inquire about getting a copy of this record." I have not yet tried to use that link, but I've always wondered what would happen ...
Let me know if its interesting!