You can probably custom make it using either bootleg or used toys. Just need to find some waterproof finish and lay some coats of it on those. This particular TBTT I was able to find here however : https://www.amazon.com/POPETPOP-Decorations-Resin-Aquarium-Ornament/dp/B085G4VYHX or here : https://www.amazon.com/Ulifery-Walking-Aquarium-Ornament-Decorations/dp/B08CKZVTCM/ref=pd_lpo_1?pd_rd_i=B08CKZVTCM&psc=1
You can also find similar aquarium TB TT toy in the "customers who viewed this item also viewed" section, and if you want to avoid amazon I guess a reverse image search could land some results ;) Overall it seems they're 15-20USD.