Checked Ameristar's website, and it actually has a decent poker page. Of course, what actually gets spread in the room may be different, but this info might be a starting point. And it includes a phone number for the poker room:
http://www.ameristar.com/kc/kc_ca_pokerroom.asp
Edit: Wherever you play in Missouri, your first stop will be the booth to get a players' card. Must have valid ID, and must have the card to buy chips. That is how they track your buy in to insure you stay within the $500 max/every 2 hours guidelines.