I used to own a Kahr PM9 with the CT laser. It looks like the laser for the Kahr uses the same design for activating the laser as for the Shield.
Perhaps it is the size/shape of my hand and fingers, but I could never reliably activate the laser on the Kahr. To get the right part of my finger on the activation switch, I had to hold the gun awkwardly. Also, the lower edge of the section where the activation switch is located would dig into my finger each time I fired the gun. It actually drew blood a couple of times.
I had considered getting a Shield M2.0 and then adding the CT laser. But, after my experience with the Kahr, I decided to go the factory laser route.
Back to the OP's question, CT and Lasermax both offer green lasers for the Shield. So, you have 3 choices for a green laser with a Shield M2.0.