Sorry, only just seen this and it's no longer May, as I've been busy with other things, but if someone wants a source of all Blenheim mayors from 1869-1968, I digitised and published online the text of The First Hundred history of the Borough of Blenheim.
The First Hundred - Marlborough Online
The text also includes the names of councillors for each year, and a variety of other local history that may be useful as a source.
The print copy of the book has pictures of all the mayors too, but I need to go back and do more work to get good scans of them, as my initial task was to digitise the text, and this alone was a huge task, done in spare time.
As far as mayors go, I've already previously contributed some biographical details of my great-grandfather, Sir Ernest Andrews, who was mayor of Christchurch.