Yes, they're extremely rare
Legendary launch pads look exactly like the normal ones, except you see the "sparkle" effect that is on the normal Pokémon that have a 100% befriend rate that you come across every now and then.
Another way to tell if you got a Legend is that the Legendary arena is the glass one in the sky that you fight Zekrom on in the beginning.
Legendaries always befriend you, as long as you defeat them. So take it easy and use a fast Poké with high defense, speed, and a good ranged move, don't forget one that restores HP.
Also, try to dodge all of the attacks that happen.
I got This from Serebii Right Here I had to long on to my account dont know if The Link Provides to People Who Arnt REGISTERED This Is All I found from 2 day search and If this isn't what you were looking for I'm assuming There isn't another way to get Shiny Launch Pad's For Zekrom
I love Weird things ¯(°_o)/¯