Threesome?

My Fiancé(of two years) and I have been contemplating a MFF threesome, she is bisexual and had brought up the idea of bringing another woman to bed with us. This would be both our first time having a Threesome and we’re seeking advice, how do we go about finding a 3rd party and for the men on here how who have encountered one what are some tips and tricks to keep the stamina up? Thanks in advance!