You may be able to also print them out. Last time I just had to e-mail them and they sent some tags, but I understand, they no longer do that. If you don't print them out, yes, you can get some when you arrive at the port, just ask the gentleman that handles your luggage and he can point you in the right direction.
Also, make sure you go to Royal Caribbean's site and fill in all your information. What ship will you be sailing on?? You may be able to also pre-book shows and alternative restaurants as well.
When you do your online "Set Sail" Pass check-in a set of e-documents will be generated and you download it from the RCI website. Access your booking and look the for 'cruise documentation' tab along the top. Go to that tab and you will see 'Guest Vacation Documents". The e-docs will include a luggage tag to print if you prefer that approach over having the porter tag them at the pier. Also don't forget to print your Set Sail pass.