Looking for bisexual provider in London

Hi all, not sure where to post this as there's no regional board for London. My girlfriend is keen to have a threesome with me and a genuinely bisexual provider. Does anyone know anybody who sees couples in London and who will be understanding and friendly? Very much an explorational thing for the g/f so it would need somebody sensitive to that.

Thanks in advance for any suggestions (general stuff re how I should play it appreciated too!)