"Such a gun needs to be of true Paradox gun type with barrels of at least 28 - a dual purpose gun".

Well, IMO, owners of such guns would probably shoot balls much more than shot. Modern made slug doubles usually will have much shorter barrels, 22" or 24", because they are actually not intended to be used for shot (maybe buckshot).
My feelings are that those looking for a modern made Paradox type of gun should also take a look at these smooth bores.
And please don't get me wrong, I would love to have a H&H Paradox or W-R Explora. It is just that maybe these Fabarms, Sabattis or Berettas are as fun as a true Paradox.

BTW, check the Beretta 471 Slug: http://www.beretta.it/index.aspx?m=74&idc=1&ids=40