Since no one took a crack at this, I'd think tracking down dies would be a long shot. I think some of the Bullard named cartridges were the same or very close to others, so I wouldn't be surprised if a more common sizing die does the trick. I'd compare a chamber cast to drawings of other full length and parts of other case dims.

For me, I'd tend to have the cases just stay with one rifle. Maybe, spot a case to figure out the hangup, then use limited areas of regular dies from other cartridges to get just enough reduction to do a decent fire forming. 

After that, see if minimal neck sizing will do the trick. I'd assume it's a lever rifle, so maybe save some notes if some taper or diameter has to be bumped back to cycle through the action, so you don't have to over work your brass. Seems like you want to shoot it, and I'd bet it's worth the hoops to jump through. Best of luck with it.