Kerrisdale was, and still is a great place for used Pentax gear. Bought my K1000 new there in the 70's and a few used lenses later on.
And, London Drugs were always pro-Pentax even in the film days - I remember in the 80's whilst "in between jobs" salivating on 2 lenses each the same price...a 500mm Vivitar mirror and a Vivitar ultra wide angle zoom (I think it was a 15-28mm) Both were only K only mount and $250 if memory serves. My friend bought the 500mm and since he passed away, I now have it as a treasured posession.
I know a former LD upper manager guy and he was a major reason they carried Pentax initially. (this was in the 80's) I think they kept up the good relations and just continued to carry their product line, and get preferred pricing so they can offer really lower prices in cameras.
Another one if you are ever in the area if you want used Pentax gear is
Reid's PhotoSource in White Rock (bought my used Program+ there many years ago). They have a dwindling selection of Pentax and other brands lenses (mainly of the film era but I did see an early digital body - a K200D I think), and if you want a dedicated
film flash, they're blowing out their old stock of Vivitar, and other brands. None that are superior to what I already have, so I didn't bite. For new, they sell the Q camera but won't do dSLRs anymore, as "London Drugs has that all sewn up" so they told me last week.