Jeremy,
Find the oldest gunsmith you can find. Forget about the ones that build custom guns, black rifles, etc, the one you are looking for is one that repairs single shot and bolt action guns for the pawn shops and financially disadvantaged customers. This guy won't likely be in the city, more than likely ha will be is a small town, not too far from a city. The reasons you are looking for someone like this are he will likely have several, if not many, similar screws taken from similar old guns. Also, he will likely be the one that will take the project on. If all else fails, he will be the one that if he doesn't have the correct screw, will know how to modify one he does have to make it work. You are correct, that the underlever should be straight, or nearly so. It has been bent in a mistaken attempt to tighten it up, maybe even by the same person described above. Once you learn all you can from the project, and have moved on to another one, you might be able to get your money back by selling it to either an antique dealer or interior decorator, or maybe a "Cracker Barrel" restaurant; you may even make a small profit.
Mike