I do not believe you can find them elsewhere but... There is hope
Look in the hardware seciton at your favorite store for picture hangers
One of them is shaped like a giant one of those tabs. If there is room you can mount this off to the side of the flapper and turn it so the "hook" part locks the tab when needed.
Or you can mount the "Finger" off a common spark plug "Feeler" gauge, or any short strip of metal, next to the flapper using a screw.. Many options. Many many options.
Here is a FREE option. Visit a Bicycle shop and ask for a BROKEN spoke, Now carefully bend it as follows.
Bend an "EYE" for the scrw (use needle nose pliars) and then bend so the wire comes straight out from teh EYE (look at a common eye bolt at the hardware, that is your pattern) now about half to an inch out bend so that with the EYE lying flat the wire sticks up
Now cut the wire off not far from that bend so you have a small NUB you can use to move it on and off the flapper.. you should get several such taps out of one broken spoke.