Any sort of buying/renting email databases is and should be considered spam. Why? 99% of the time when I subscribe on a site, there a big message telling me “WE HATE SPAM. WE WILL NEVER TRADE OR SELL YOUR EMAIL”.
I don’t care if I have quadruple opt-ed, I have not agreed for someone else to obtain my email and send me promotional material.
To answer directly I doubt you can bye such emails anywhere. I doubt anyone can prove to you that these gamblers have signed up and have agreed to receive emails from ANYONE. Your question shouldn’t be where can I buy from, but What can I do to get more sign-ups myself.
Sorry if this is not what you wanted to hear, but buy/selling emails has always been something affiliates and players hate. (especially universal4 
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