They are in the trash can by the tour guide.The trash can with the lid off
You can look around the island all you want. The "Underground Tunnel Tour" requires tickets. (see related question)
Look in the round trash cans to the right of the Tour entrance. Move the trash out of the way until you find the tickets.
The two tour tickets are in a round trash can to the right of the Tour entrance. Dig down through the trash to uncover them.
They are in one of the two trash cans near the Tour entrance (under the garbage).
In the second trash can to the RIGHT of the tour place then go to the man in the internet cafe.
in the trash can next to the tour entrance then bring it to the guy in the Internet Cafe.
The can with the tickets is the round one just to the right of the Underground Tour entrance.
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.
If you go where the tour guide is and go to the right there's garbage cans there
take them to the tour place
There are 2 tickets at the bottom of one of the two large trash cans to the right of the Underground Tour entrance. (Dig down to the bottom.) (see related question)
Although the girl has sold out, you can find two tickets to the Underground Tour in the second round trash can by the Tour entrance. You should return them to their owner, who is at the Web Browser Cafe on Main Street.