Welcome to the forum from the East Coast.
Buy an inexpensive GS-100A and wire it in. I have them on my Honda and my Kawi.
Under $20Cdn and ships from Amazon in Canada so no long overseas delivery waiting.
I bought these:
BlyilyB 12V Flash Strobe Controller Flasher Module for LED Brake Light Tail Stop Light (Pack of 2) : Amazon.ca: Everything Else
Here's the flash pattern on a video of my bike. It only flashes this pattern, 4 fast, 3 slower, then steady on.
I only have the flasher on my extra brake lights on this bike.
Here's a how to video someone did on a car.
I've obviously also upgraded my bulbs to LED for the full effect. The gs-100a is designed for lower draw LED's. They also make a model for higher wattage incandescent bulbs.