Please help me find the perfect video for her.

You could sort thru the videos on xHamster.com under the “cuckold” category to see if there is something that might help her along.  Usually the ones similar to what you describe as your wife’s fantasy scenario are very amateurish and not very well done but there may be something she’d like.  Another video source is slutwives.com but there again, it’s pretty much the same story.  Good luck.