I will dispense with standard "why change his mind etc..." and instead try to answer your actual question.
They have an excellent scripture reference here on the home page:
click Resources->Biblical->Scripture Index (see attached pic)
I've had decent success shocking people with Moses.
What I mean, is most people do not realize Moses himself was polygamous. This takes away the "G-d just permitted that then b/c people were dumb" argument - lol.
You just come back swinging "So Moses, when his face was glowing because of his closeness to G-d, was G-d just tolerating Moses' polygamy?"
Another fav of mine is, when the prophet Nathan rebuked David for the Bathsheba issue, and basically says "If you had wanted more x,y,z, or women you could have just asked, surely I would have given them to you"
So how is G-d Himself now "tolerating" by answering prayer directly by "giving" what's "tolerated" (sorry got quote happy there, imagine my fingers in the air making annoying quotes).
I also like to hit 'em with Paul's control of who can be an deacon having something to do with polygamy. It doesn't matter in this context if he's truly saying polygamists can't be deacons or not, the point is he's acknowledging that there are active polygamists in the body. I think it's a specific situational control there but that's for another post. The question comes down to "why is Paul regulating if it's non-existent outlawed by Messiah?)"
This all assumes your hubby likes to discuss things in that manner.