A very difficult task as there is no single database likely to have this information. The CAA website includes UK statistics but it is slightly out of date and doesn't give the full picture. There are over 70,000 PPLs in the CAA records; but they have no real idea how many are actually in use, other than to count the number of valid medical certificates, the
2008 figures are about as close as you will get.
You would need to go through every Aviation Authority in Europe to see if you can find similar figures. The JAA had no records and EASA does not intend to either.