Thank you for answers.
On further investigation I found out that the spare number of the L500 keyboard is K000077780, while the number of the P200 is K000050540.
I just called the Toshiba Support and got the answer, that all notebook keyboards have the same connections and spare numbers vary anyway on local layout. As the flat cable should be identical, the only problem might be the position of the connection. The service guy compared a P200 and a L500 and said the position of the touchpad is exactly the same, so it should be possible.
As I can get the "P200-keyboard" for 20 instead of 40 € I will give it a try. I'll be back and complain if it is not going to work
