Here is a link to a wikipedia entry about the "Universal Nut Sheller" developed by Jock Brandis. It seems like such a simple design that it could be used for larger nuts like the Black Walnuts with a few modifications. It is a great approach because it can be adjusted. It uses concrete molded into a tapered cylinder with a tapered cone that fits within it. The distance between the two can be adjusted in fine increments making it possible to get just the right fit for any diameter shell.
Hope this helps.
I thought I would give a report that the elderberry and hazelnuts did very well beneath the black walnut one year later. The most notable was that black raspberry that spread voraciously and produced many berries. This year it looks that the the gooseberries will really take off.