Stumbled on this old thread and figured I’d share my experience - I too went on a hunt for mastic tape in HRM / Nova Scotia and turned up empty handed.
Stopped by a handful of electrical supply stores and none of them stocked it, and called emailed a few more. Most said I’d need to order a case of it to be worthwhile for them, so a couple rolls was out of the question.
I ended up ordering online - the price is tough to swallow (watch for price drops if you have time, they will happen), but I tried the tube wrap and it was tough to get right with my bike / level of patience at the time.
I did the chainstays on my / my partner’s bike and there’s still plenty left.