Double vaginal is something that we do quite often...I've never been turned down by a gentleman when I asked if he would be interested in indulging me in this
Now...I have felt them out throughout the night prior to playing asking what their feelings are toward incidental touching between the males, what things are off limits to them..and so forth. Occasionally there will be a gentleman whom I can tell won't be comfortable with DV...so I don't ask.
So...to answer your question on how easy it will be to find someone to help out with this...not as hard as you might imagine. Just ask...the worst that can happen is they say no.
Teresa