Well as far as the "legit" branded Banshee, those definitely aren't that rare. The ASC branded OM-117 is something you don't see many of, and even fewer OM-120's. I have never seen a dual toned grey OM-117. I believe ASC had stopped marketing/producing the dual tone stator just because the P-15/RM-127's are a lot more effective with that large single toned stator. Keep in mind these came out in the early 90s (IRRC) and the governmental desire for dual toned sirens had fallen with the Berlin Wall.
Just as you see many more P-15's than you do Banshees, you see many more RM-127's than OM-117's, The RM-127 is louder and has a larger coverage area, which is why they were likely much more popular than the omnidirectional. Very soon after the switchover from ACA it didn't take long for the battery upgraded versions--The RM-130/OM-120 to come to market, and it was only for a couple minutes and then the Tempest series was branded and those sirens were essentially garbage because they took like 6 batteries to run.