Bummer. I'd be tempted to see if a framebuilder or welder in your area could fix it, but then you're out $$ and out of recourse if something does happen.
It might help if you gave us a few more parameters to work with. How "offroad" is offroad? Gravel, dirt, singletrack, something else? IOW, how wide a tire do you want or need to ride? I'm guessing you'll want mount points for a rack and fenders? Anything else we should know before you get a complete listing of "bikes with a frame larger than 61 cm"?