http://ticket.toureiffel.fr/ Any other links lead to information only or tour-type tickets.
Try this one.
Hi Victor, this is the official website for purchasing tickets:
Sam & Donna, thanks for replying, but each of your addresses took me to an information only website that I tried originally on my desktop PC using Explorer 11. I just tried both of those on my laptop which has Explorer 8 and it found the ticket website. Maybe it has something to do with my desktop web browser. Possibly others may have the same problem. If so, this might be the solution for them as well.