It's hard to keep stats of the number in the monthly anti-Scientology protests those days, since they are not rounded up anymore, and they are not always reported for individual locations either. I guess it would be possible to draw a figure but it would take an awful lot of time. Not worth it.
To have an idea, though, I have taken a quick look at the Dec 13 entries for the London post game, as London was always by far the biggest player in the field.
If this post is true, and there are no other entries about numbers (really I did not wade in all details through the 9 full pages posted that far), then we are speaking of a maximum of 20!
This for a location that peaked at 725 in March and was still at 566 in July when all the rest of the world took the plunge, and was still at 120 back in September!