I'm currently checking the web site www.alcatrazcruises.com to book an Alcatraz tour 2 weeks from now but they are fully booked. Is that web site the only way to book a tour of the island? Will it be possible to show up at the pier and getting on a ferry there to the island?
The National Park Service has an arrangement where only a single company is granted an exclusive franchise to travel to or take guests to Alcatraz. Therefore, if you want to go to Alcatraz, there is only one company you can travel with, and private boats are forbidden.
Tickets for the Ferry to Alcatraz are available at the Alcatraz Cruises website, but they sell out fast so buy in advance.
There are a few other websites when you search, but I can't vouch for any of them. What you could do to confirm is to call Alcatraz Cruises Box office: +1 415 981-7625, or email them (email@example.com). However, even when I was in San Francisco last year, tickets were sold out online and it wasn't possible to buy them in person on the day. However, that was Fleet Week, so your mileage may vary on a different week. I'd drop them a line and see what your options are.
This is what happens: one company is responsible for selling all the tickets to Alcatraz. The thing is they sell a lot of tickets to multiple tourism agencies. These agencies create some packages like Wines + Alcatraz and sell them to the general public. By buying one of these packages you can get second hand tickets to Alcatraz.
If there aren't tickets anymore for the date you want and you are not willing to buy those combos there is still one thing you can try: check the official website one or two days before your desired date. When the tourism agencies fail to sell some of their tickets, those tickets are returned and put back for selling in the site(you may want to refresh the page every 5 minutes to find the ticket before someone else does). I managed to get a ticket this way. The bad part is that usually only the tickets for the worst times are returned.
No! It is possible to line up very early in the morning to try to get last-minute tickets. This is a desperate last-ditch move where people show up as early as 4am to get in line for when the ticket office opens at 7:30am. Everyone buying a ticket must wait in line the entire time (no sending someone ahead to buy for the whole group), and you could well wait in line for hours during a wet and cold morning to wind up with nothing, especially during peak season.
Obviously, getting tickets through a more expensive package (you could even "throw away" the other part of the package if you want) or one of the returned tickets as hooray describes is a far better option, but if you want to try it, the details of the system are provided online. The short version is: get there extremely early, everyone buying a ticket must wait in the line the entire time (except restroom breaks), first come, first served, no guarantees.
It's probably worth talking to the Alcatraz Cruises workers at the ticket booth before trying this, to ensure the morning-of scheme is in operation.
The best approach, of course, is to buy your tickets from the website months in advance.