Where can I find speed and thrust data for airplanes during the approach?
All you need is collected, though not published, in airlines' Flight Data Monitoring (FDM).
Airlines collect a load of parameters for training and statistical purposes. If you can contact an airline, tell them what you're doing and make it sound like you could improve fuel economy, there's a good chance you can get some of the data.
Another place to seek would be aircraft manufacturers like Boeing or Airbus.