I just went to the Carnival site and couldn't find info. about irons either! Just that they are available in the laundry rooms. They have redone their site recently so maybe they missed this. This info. used to be there. From what I have heard, NO ship allows travel irons due to the fire hazard.
I recently tried the Downy Wrinkle Releaser (bought it at WM) based on cruiser's recommendations on this site. I thought it couldn't possibly replace ironing. It really works! You might want to buy a bottle and try it before you leave.
I hate ironing-so this is wonderful!
Your cabin steward won't say anything about anything "illegal". They want their tip!