Searched for lots of divers. Never heard a whistle (over radio, engines, inside, etc) in my life. I have a deal for you. I will send you (for the cost of shipping) a waterproof case made of Delrin by Light Monkey or a screwtop case made of PVC with a whistle, mirror, I think I have some orange marker dye, and a PLB with expired batteries. It isn't a joke, you can buy a new PLB or SPOT, or whatever makes you feel safest if you promise to carry it on every dive.
I have half dozen of them I used to use on my tech divers. Since I no longer have tech divers, I am willing to part with these to enhance safety of folks who tend to dive alone far from help.