Guessimates!
I'll give a guess: 13,000 Commercial Pilots, 1,500 not employed. Of the latter, there are many who are not looking for work and also many, who have looked but have had no success. There are also quite a few that you would not want to employ in any capacity! Let's guess at say 500 actively looking. However, the people in the know should be the Campaign in Gatwick Towers. And maybe they are the people to ask. After all, we do pay their wages!
But don't compare us with Oz. There are many pilots with CPL's (and I'm one) because they are relatively cheap to get. But there are only a few jobs because of the position of Oz and it's relatively small population.