Hi Paul,
We appear to be researching the same family. I am descended from one of the NZ Maitlands and also a direct descendant of John Maitland (Snr). I have been researching the family for about 30 years and inherited older trees from my grandmother's cousin who did a lot of work. I had suspected Alexander Maitland was an older brother of John. I also believe that he was named after Ann Grey's father as there is a baptism record for her with which fits the date of birth with Alexander Grey as the father.
I have been mainly working in Familysearch and have recently had another look at Alexander Maitland. I have put together the findings and have added him to the tree. The clincher was the mention of his father on his second marriage certificate and his father's occupation. As you are aware there is a strong connection to the publishing firm of Blackie and Sons.
Here is Alexander's link in family search:
https://www.familysearch.org/tree/person/details/LTD6-36CI have also been attempting to link the Maitlands and other branches of my family via Find a Grave. I found the record for Alexander's burial and have made the record and links for him just prior to finding this chat.
https://www.findagrave.com/memorial/234162216/alexander-maitlandI hope you find this useful.
Regards, David