Getting game passes in a place?

Hi guys, I was wondering how I could get the game passes of a place that are on sale. I'm trying to create a shop GUI which updates if a game pass has been added or removed and so far, I've not found anything I can do to achieve this.

I did some digging, but only a found a link of a ROBLOX Web API, which I can't use because ROBLOX disallows HTTP requests to the ROBLOX domain. From there, I'm stumped as to how I do this without doing it manually.

Any help is appreciated, thanks!