It seems to me that various fairly ancient heavy walk-behind slashers have been a feature of most clearing sales for many years. Every old farm has one or two of them in a semi-defunct state in one of the sheds, and doesn't use them because it is easier to use the tractor slasher. Bringing those things back to life is probably not very difficult - they are just about indestructible, and have been ignored because they are seen as old-fashioned, not because they are broken to any serious extent. Unlike, say, rotary hoes, they are neither complicated nor subject to heavy operating loads.
Personally I wouldn't have any interest in a modern one when the old ones are more interesting, more durable, and a whole lot cheaper (like, almost free).