I agree with the idea of using bulk XTP's. They are relatively inexpensive and a proven bullet on deer sized game. I would suggest getting them in 240-300 grain range, in .45 cal (.452). I'm not sure about your Huntsman, but I found that in one CVA rifle I owned, there was NO sabot made that I could match upwith a .44 cal bullet and get it down the barrel. As soon as I switched to .45's I found three that were loadable.
As far as locating the right sabot, you could get a pkg of Harvester Crush Ribs (black), and go from there. If they're too tight, the only thing I know of that's thinner is MMP's 3 Petal sabot. If they're too loose, you can get regular Haversters, Hornadysor MMP's - some of which have already been mentioned.
Good Luck and Good Hunting!