Doesn't look like they are available to book yet. I wouldn't be concerned; no way would any cruise company miss an opportunity to upsell excursions 😉
In the mean time, it might be worthwhile looking at the port reviews elsewhere on this site. Pompeii, for example, I've read is easily accessible by public transport. Also - for my situation at least - a taxi may be a better bet for Mt Etna, given that the weather and hence views can be very variable.