I haven't seen any Gamblig Platform who used Telegram for Promotions, most I know is that they use Discord.
Do you have any Idea why they don't have any Telegram Communities? and why does it seem they don't use this platform for their promotions?
actually there is one that becoming more popular now mate and that is Earnbet
https://earnbet.io/In which they have telegram Group and continues to grow community
Their telegram group is
t.me/earnbetcasino
maybe you should try visiting their Group and see how active their telegram community and the players as well.