Bombastulin

I completed Spines of America quite some time ago, but have not been able to start another story mission since. I have been back to camp and talked to John Marsden a good 20 times, over a period of a month or two, as at first I thought you just had to wait some period of time for him to "get better." I've explored 3/4 of the map, have hundreds of dollars, upgraded gun & horse, but all Marsden has for me is small talk. I really have no idea what to do or why it's not triggering. Any tips?