I have to say I'm not surprised at the lack of response at all lol. Maybe I'm projecting my own opinions on to this but I'd guess 99% of punters see this as a very solitary pursuit, and would be pretty mortified if their friends/casual acquaintances knew about it, let alone their missus.
I suspect most people who want to branch out as a couple do so as swingers, rather than seeing WGs.
'Hey hun, I think we're both agreed we really want to shag other people ... swing for free or pay someone £120 an hour to pretend to be up for it, what do you think!?!?'