To be fair - I haven't looked for boys only clubs - I have a DD so no need at present.
I have just had a look at my local towns Mini Rugby club - ages Y1-Y7 - not a single female in any of the team pictures. It doesn't specify you must be male, but it seems to naturally fall that way. Our football club also trains separately (I have a vague recollection there is an age at which the FA ban then from playing togther) but I am aware these are two sporty activities so don't fit the bill.
Boys Brigade now seem to have the option of having a girls association working alongside them so that also seems to be area based if it boys only and I am sure some will object to its religious basis as well, which is fair enough.
It is something I feel the boys should have access to - I really don't have an issue with that, I don't have an issue with boys having there own space, I agree they need it just as much as females.
I just don't see why Girlguiding is getting the blame for not changing its policies. The Scouts changed their policy for reasons stated previously - lack of numbers, falling youth membership, at the time they were competing with lots of boys only groups (early 90's) which again were sport related but did reduce the numbers who could attend.
Lots of us have expressed why the girls benefit from space away from the boys - I admit I work with the older age in Girlguiding but we aren't just all about crafts and sewing as others have pointed out, we do also cover some bigger issues in a fun way. Lots of things which even within a school environment we would split into genders to discuss to enable both to be given a fair say (am also a secondary teacher who does a lot of PSHE teaching)
Boys do deserve it as well, but taking it away from girls doesn't solve the issue as it means no one gets it.
Scout groups, if they have the numbers and leaders, are allowed to have a mixed section of each type and a boys only section - but then the focus of the groups changes as well. I am not sure about the programme planning within Scouts but at Guides the girls have a lot of say over what we do.