There are lots and lots of rare and supper rare cancels on Canadian stamps...Here is one that would almost be impossible to find.
The town of Mount Pearl in Newfoundland had postal station called
Mount Pearl Sub NO.1...It was
opened Oct.18th,1966 and closed 8 days latter on
Oct.26th,1966...See attachment below.

Below is the house that was used for a Sub Station for 8 days only..Obviously it was changed to a residential property.
If anyone comes across one, I will gladly purchase it for my Newfoundland collection.Robert