If no satisfactory responses here, I'd drop an email to City Theatrical. After all, they make it, it would be in their best interest to ensure there's a symbol for it so designers can specify it. Also, I bet it's included in one of the SoftSymbols libraries; @MrTemplate could tell you which one.
The last SoftSymbol library I used had a beam-bender symbol. It was a right triangle with a slightly thicker lineweight on one side. I would roll your own if you want something fancier than that.