I am doing some statistical research about bicycles and riders. Now I need the peak power or max power and critical power of riders (professional or non-professional). But it seems really hard to get. Where can I get these data?
Getting data on professional riders is harder now than it used to be: in the past, teams and riders would sometimes post their data on Strava or in WKO format. I suspect, but do not know, that this was done in partnership with sponsoring power meter manufacturers as a way to generate interest in the product and the types of analysis one can perform with power data. I also suspect, but do not know, that this is less popular today because the use of power data is more widely understood, so there is less need to publish the data as an "advertisement" for the product. For example, recently Remco Evenepoel briefly published his power data for a race, then shortly thereafter deleted it from view.
That said, there are far more non-professional than professional riders and, depending on your research question, it may be the case that you can use non-professional data. The simplest and best way, of course, is to get a power meter and experiment with analyses of your own data. However, at some point you are likely to want to broaden the scope of your analyses and check your results with a wider sample.
At the moment, a good resource is the Golden Cheetah OpenData Project. There may be others but I believe that now (February 2022) there are about 6000 unique athletes who have contributed a total of around 2.4 million activities to the project. In particular, for each of these 2.4 million activities, you can also download peak power for durations from about 1 second up to 10 hours. You could then use these data to produce estimates of Critical Power and W' using different estimation models. A short description of the data set and how to access it can be found here.
An additional resource could be Zwift e-sports data for their recent "pro" championship series. Some data on w/kg by duration can be found here, though the data format is unwieldy so would need some re-organization.