its in the open trash can in down town.
you get the ticket from a garbage can
you go to main street and there is a garbage can with no lid on it then at the very bottom of the garbage can then you go to the news place and then you get a ticket from him
You go and show it to the dude that ask you to find the ticket and then he will take it from you, then he will give you one. After you got a ticket go the person that's next to the tunnel and show it to her.
When you chase him through the streets, he jumps into a boat at the dock and drops his key card. Then you can get it.
In the trash can
The man you give the ticket to is in the Web browser Internet cafe on main street. Go to the right and find a man with an orange beard. When you give him the tickets, he will give you one.
look in trash can move trash aside and you will see it.
run like crazy
In the bin near the tunnel entrance.
dig in a trash can and there is a ticket. the character wont let you use it
The tickets to the Underground Tour on Counterfeit Island are at the bottom of the round garbage can to the right of the entrance. Once you have them, you have to return them to their owner, who is at the Web Browser Cafe on main Street.
You can't get passed them. You go into the tunnel and figure out that picture then when you do, you find yourself back in the museum. I could tell you the rest but that's another story.