Unknown to me till today there is a country in the world which did release season 3 of SeaQuest DSV, or SeaQuest DSV 2032. Thanks to someone from Australia who told me this via twitter by pure coincidence! October last year it has been released on DVD.
There are no English subtitles on it. Price online is a bit high though, appr. $40 without shipping. This is a region 4 DVD but are also compatible with a region 2 DVD player. Season 3 contains 13 episodes.
Update : Apparently it also has been released in France, but unfortunately only French language and no subtitles.