Several members of his family are in Iran. I would not be surprised to find that he is there.
On the other hand, Baluchistan crosses the frontiers of three countries, and gives him the chance to move from Pakistan through Afghanistan to Iran as he needs to. So maybe you're right.
Why would Iran stick its neck out for an unpredictable Sunni nutcase, who, if found by the US, Israel or anyone else to be in the country, would only lead to the immediate elimination of the present regime? The Mullahs are a problem, but they're hardly stupid and harboring Bin Laden is about as stupid as anyone could be.