Possible locations.

'A gentleman never wears brown in London'

Looked at the idea of the old Gentlemans clubs - A gentlemen's club is a members-only private club of a type originally set up by and for English upper-class men in the eighteenth century, and popularised by English upper-middle class men and women in the late nineteenth century. Today, some are more open about the gender and social status of members. The original gentlemen's clubs were established in the West End of London. Even today, the area of St. James's is still sometimes referred to as 'clubland'

The problem with trying to stick the posters up in this area would be that they are posh areas which could pose problems.

(Old clubs such as Boodles or Whites around St. James.)

Or we could look at modern day 'Gentlemans clubs' (now called Private members clubs) such as Soho House London
40 Greek Street
London
W1D 4EB