I think you sell yourself too short. You have a great reputation in the field and that alone would be enough I think for a publisher, especially if you present them with an outline of the plan of operations and what got left out with examples. A good university press is supposed to go for stuff like this and, speaking as a businessman with lots of marketing and sales experience, these sets would end up in most university and large public libraries alone, would would be sales of several thousand sets alone - then there are folks like who post here that would want them - especially if they could come in under the price that Broadfoot had.
I think there is a demand for more of this material and a new set of books would fill in the gap especially when you show a prospective publisher what was left out.
Greg Biggs