Probably Amazon, or a store that sells home decor like vases and stuff. I think I've even seen similar things in pet stores a couple times. Not sure where you're located, but I just searched "wine glass fish bowl" on US Amazon and found this that looks pretty close. Found similar items on AliExpress by searching for "giant wine glass". I'm in Canada and I occasionally see giant novelty wine glasses at places like HomeSense and Winners, sometimes even at secondhand shops.

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Edited to add that anywhere that sells "wine mom" type novelty merch has a pretty decent chance of having something like that, too.