I didn't quite understand what you want, but ...
If what you want is the cast of all seasons then I think it is still not possible.
As I recall, an API Request will only return the cast from last season.
I think there are plans to get the full cast, but it hasn't been implemented yet.
See here
https://www.themoviedb.org/talk/5e25b1991bf2660016fd6386
And here on the To-Do list on Trello.
https://trello.com/c/gDhgYSPx/23-implement-the-new-tv-aggregated-cast-crew-views
You can vote for the Trello item.

@Vishalt1 Are you looking for the newer aggregated cast view found here on the website, or are you trying to use with_cast on TV discover?