Mustang makes a seat that is an inch lower, but it is also an inch farther back, so it may give you problems with the bars. You might look into a custom seat that's lower but the same distance to the bars. There are lots of reputable seat makers with a quick Google search.
Oh and by the way, there are also more expensive options, like buying the shorter progressive front springs, or the lowering link and a shorter rear shock. However, that seems like a last resort to me because it takes some travel out of what I consider an already moderately harsh suspension, and it might also limit your resale market to the shorter inseam crowd, making it somewhat more tedious to move once the time comes.