Honestly, I wouldn't waste your time with a new one. It does not affect the performance of the wiper itself nor does it make it any weaker. I have always been frustrated by that tab because it makes replacing the insert and cleaning the glass a pain. I broke mine when I was washing the 4Runner and carelessly pulled too far back on the wiper arm. It hasn't affected anything and honestly, I like being able to pull the wiper arm further back now. I may take it off and sand the broken section down so it looks more factory.
But if you insist on getting a new one, Junkyard, salvage yard, or even online should be able to get you a replacement rather cheaply.