There is a continuing IASPEI project (which should be nearly finished by now) to provide the third-level regionalisation of the world, which will be the finer divisions that you need beyond the F-E ones. Each country has its own expert for constructing the third-level regionalisation for its national territory. I don't know who's done it for the USA; I was responsible for the British Isles (by agreement with the Irish Republic).

Once everything has been finalised I expect NEIC will start using it.