I agree with you entirely that this appears to be a clear cut case of retaliation, as they are suspending for a nonsensical reason so soon after you met with the tribe's attorney.
As what you were disciplined for happens on a regular basis and you were just subject to discipline for it (and have never been disciplined in the past), you definitely have a great case for retaliation for reporting the sexual harassment you experienced to HR. (I also agree that it makes no sense for you to have been disciplined for this, as you were doing the right thing here, and it is something that other floor managers would also do on a regular basis out of necessity).
I would definitely suggest that you file a complaint with the EEOC regarding the sexual harassment you were forced to endure and the retaliation that you suffered once the complaint was made to HR (even though you didn't initiate it yourself).
Due to the time frame between when you spoke to the tribe's attorney and when you were unfairly disciplined for this 'violation,' you have a great case for retaliation on top of your case for sexual harassment against the casino.
You can and should file a charge with the EEOC for sexual harassment and retaliation. You can do so using the information available online here: http://www.eeoc.gov/employees/charge.cfm
The EEOC will investigate your complaint on your behalf and either file suit on your behalf or issue you a right to sue letter so you can pursue your case against your employer through a private attorney.
I hope the above information is helpful!
Please let me know if you have any follow up or clarifying questions, as I want to ensure your complete satisfaction with my service. Thanks and best of luck!