Greener,
The reason that manufacturers like H&H dont produce guns with left hand opening levers is the cost and hassle.A special action machining would need to be made with the spindle and lever hole going in the opposite direction to normal.As this would be a one off action,rather than being made in a batch of say 25 as is normal,and the bolt would need to be made with the spindle connection the other way round,the cost would be pushed way above normal and the disruption to normal production make it not worthwhile.In saying that some of these guns do exist,but are very rare.