NEC doesn't provide firmware for their drives officially.
But they provide them for their OEM partners (companies, who sell Nec drives under their own name). MadDog is one of them.
So, you can use the MadDog firmware for your drive too, because they are identical. I'm using the MadDog 2.F9 for my Nec 2510 with great results. It has the latest writing strategies, supports Bitsetting, is region free and has no riplock.
(If you don't know what theses words mean - use the search function )