Why not buy a decent broadcast spreader, some of them go over 100ft. Cheaper than an air cart plus you neat looking machine. The newer ones from Europe are very very accurate lots of them starting to show up around here. spreaders can go 15-18 mph, 1000 ac a day is no problem assuming you have a good tender truck keeping fill times to a minimum.
As for the patents my guess will be you have to approach a company that specializes in application equipment and see what your patent is worth. I suspect not a lot, nothing really special here unless you have a real novel deflector or something. (sorry) Lots of homemade applicators like it around,
spreading fertilizer is generally weather dependent and need to be able to get a lot of ac done in a day.