I've read a couple of articles from the The Washington Post that have talked about Europe and Australia's response. There was a study done in Australia which had done a gun buy-back program. In the place with highest buy-backs there was both a large drop in mass shootings AND a large drop in suicide deaths. Perhaps adding this benefit to the conversation would move things along.
To tweak that slightly, I think establishing a common set of goals would be instrumental to having a productive dialog. Regarding buy-back, if that were to gain any traction here, it would have to be clear from the get-go that it's an optional program, not a seizer.