That's what I did with the old (pre Columbia Sportswear takeover) Montrail Hardrock. I kept doing internet searches and buying single pairs from shoe dealers around the country (even one from a shoe store in my old hometown of Laramie, WY). I am now on my last pair (the one from Laramie!), unfortunately. I can also get a great fit from New Balance SL-2 last with motion control, but that last with added motion control doesn't come in a trail runner with lug soles. To those I add green Superfeet. However, I'm now past strenuous hikes (age), so the soles in regular NB running shoes seem grippy enough for most places. And there's quite a bit of wear left in the last Hardrocks.
May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view--E. Abbey