I would not necessarily recommend Oslo Taxi. If you choose them, make sure your guide is certified, and that it is more than just a taxi driver that's gonna show you around.

Bislet Limousine should have some services that might suit your needs. I would contact the Tourist Information(They may be called "Innovation Norway" now) in Oslo, and ask, they should(they better!) know who you can use. The concierge at your hotel should also know about the available offers.

EDIT: Forgot you were staying at a cruise ship.