Well, who knows, Vergil might be looking for him right now.
Btw, the Reason I said this, is because unlike Dante, Vergil was the one who knew all about the story of Sparda's betrayal, and what happened to him.
If you think this through, Sparda was only punished AFTER erasing the memories of his twin sons, and hiding them, unlike Eva who died in front of them (or at least we can assume so).
That means, Vergil had no means of remembering Sparda's tragic fate from personal experience, since he never actually witnessed it, just like Dante.
There is even the possibility Sparda turned himself in, for the sake of Dante and Vergil not being so easily found.
But back to my point, Vergil gathered a lot of information after recovering his memories, and maybe he actually found out "where" Sparda was imprisioned, but realized it would be (at least by his point of view) impossible to get him out, or even get to the place at all, specially with Mundus controlling everything with the Hell Gate imortality and such.