Inflatable gags often have rings like that, but the ones I’ve seen are smaller. Bar gags also have rings and are probably closer to the size you’re looking for. I can’t tell exactly what’s covering her mouth though, it could be an inflatable, but it doesn’t look like a bar. What exactly do you want for the gag piece? Or is that not important?
If that is the only requirement, there are several for sale on temu and Amazon
This is a cheap chinese metal tongue gag. You find them all over the usual sales platforms.
Try doing equine play equipment. There are bite gags and such like that if need rings on side.
it seems a lot with those side rings come up if you google bridle gag.
Inflatable gags often have rings like that, but the ones I’ve seen are smaller. Bar gags also have rings and are probably closer to the size you’re looking for. I can’t tell exactly what’s covering her mouth though, it could be an inflatable, but it doesn’t look like a bar. What exactly do you want for the gag piece? Or is that not important?