Internationally, I doubt a politician will disclose this kind of business he owns. Its one they wouldn't be proud of.
Exactly. Gambling isn't legal everywhere. Some countries legalized it, while some other countries even forbid Gambling and forget about opening a casino. Yet, some politicians may own local casinos. Even if it is forbidden, politicians may own their casinos secretly. As you may know, Gambling is banned in my country, but law enforcement agencies found some casinos in elite areas.
Mostly, the political leaders live in that area, and the casinos have been there for a long time. It is believed that all those local people knew about that casinos. Since some political leaders were sheltering them, no one ever dared to report about it.
We would provably get an idea if politicians owned a gambling platforms in their country if there are monopoly happening and they don't want the other players to enter the scene. But if there's rampant gambling activities in those countries or maybe even the regulation is strict and they ban all gambling platforms to enter in their country then maybe we could speculate those politician doesn't own any business related to gambling with these reasons.
Also same as what has been said I agree that no politician will disclose about their participation on a gambling business since it can possibly ruin their reputation.