While researching worldwide numbers for our application to the Commonwealth games in 2001, the association secretaries in the various countries gave me: England 120 clubs and 3500 members; Wales 3 & 76; Scotland 9 & 130; Jersey 1 & 50; Australia 277 & 6641; NZ 136 & 4000; SA 14 & 200; Canada 11 & 300. TOTAL 571 clubs and 15,097 members.
You could add in all those countries like Belgium, Spain, etc. quite easily. What do you do about USA? They play a funny version. And if it comes to that so do China and Japan.
In some countries there are clubs that are not affiliated to their national associations, but I don't think this has a great effect.
So, a reasonable estimate today would be about 16,000 regular players of association and/or golf croquet.
What proportion play in tournaments? I don't know. And what is a 'tournament'? Do you include internet club events?