Depends on how much capability there is locally. You can add internal braces and then weld. You get pieces of reasonably stiff sheet metal and curve them over something or oval out a 1/16" wall tube. drill two holes above and below the joint and use sheet metal screws to pull the metal tight. Them rose weld the other holes. Remove the sheet metal screws and rose weld the second holes. Then weld the whole joint area solid to the internal bracing and itself. Velos point about the condition of the metal is a good one, if it is all rust you have a much bigger problem. This kind of weld can be done with any of the major instruments, TIG, Stick, Mig, or gas, the key bit is a welder able to weld thin material which is what autobody repair is about. The other problem is getting it well enough lined up to work.
Another is to find a fork that is reasonably similar, cut it off at the crown and weld it to the front of the other fork. Not saying this will be a beautiful thing, but it would be far simpler to do and would have some chance of coming out straight. You would end up with some more fork offset, your bike would not only be heavier but a lot less nimble, but it might track and not fall appart. The other advantage is that when stitched on well you can probably unstitch it and even repair the fork you have later, should that be the kind of thing a frame builder could do for you if that was your current option.