Seasons 1-3 are available on DVD, but they came out pretty sporadically (2005, 2006, 2009). As far as I can tell, there are no future release dates for the remaining seasons (Unless you can tell me differently). The only other way to speed things up is for fan demand, because they won't spend the time and labor to make a product they don't think will sell well.

You can help by emailing Sony at stockfootage@spe.sony.com (obtained from http://www.sonypictures.com/corp/cliplicensing.html#2) And simply state you'd like to see the final seasons of The Nanny released on DVD (or BluRay).