Best way you'd advise to track down a specific garment (women's)?

[BigBrother]

I saw something come up on IG the other day and it'd be perfect for my girlfriend's upcoming birthday. Unfortunately it had sold and I've been coming up empty thus far finding another instance.

I've searched eBay, Etsy, Poshmark, and IG using relevant hashtags. No luck thus far. Where would you advise searching/posting?

Thanks so much!!