u/Ok-Cost-5324

I cannot for the life of me find the proper replacement or even the drain portion for this. This is my children's tub and we have to use a rubber stopper for bath time. I have attempted to find a plug or even drain replacement for it but nothing works. Ive tried some of the "universal" stoppers thay you just push in and its supposed to work but the drain is too shallow for any of those. Any assistance would be greatly appreciated.

I do NOT have access to the piping to change the entire setup. This tub is on the second floor directly over the stairs.