I just submitted my order for my husbands tuxedo for RCCL Voyager of the Seas next month. You can order it through RCCL web site www.royalcaribbean.com
under gift catalog, tuxedo rental or through www.cruiselineformal.com
either way its the same since RCCL website just redirects you to the other. If you don't want to order online you can call them at 1-800-551-5091. You do need to call if you want to order a tuxedo for a child.
They offer a couple different packages. For example you get - 1 Black Jacket, 1 Black Pants, 2 white shirts, 1 Cummberbund and Tie Set and 1 Set of Cufflink and Studs for $85.00. Then they also offer for an additional cost, Vests ($15-$20), Shoes($12), Socks ($6) etc.,
Once you place your order they will have the tux waiting for you in your stateroom once you board. If there is a problem you can have it altered aboard ship.
Hope this helps.