I had about 80 Code 3 2100s in my fleet with those awful bulb lights, none of them had flashers. Not saying it wasn't an option, just none of mine had it.
We use to flash halogen take downs with a headlight flasher with high beam override. You could do the same with alley lights but both L and right would go on at the same time.
Code 3 also makes the 900 series flasher, on which you can flash or steady burn both td and alley. i actually have one in my jeep that i use for led lights