I tried to book a tour of the Vatican museums, St Peter's Basilica and the coliseum with a RS's recommended tour group (Can't Be Beat Tours) but they require a minimum of 10 guests. I've done a lot of research, and the price was reasonable & the reviews were good. Please let me know if you are interested. Thank you.
Vep have you heard of cruisecritics.com.. they are a cruise forum.. frankly the biggest and the best. You can find your exact ship and sailing date and post on a forum just for that.. plus they have individual forums for each cruise line and each port . Many people try to split private tours etc. Good luck.
Pat is right. You need cruisecritics.com There's no downside to registering.
Go to the "roll call" section to find RCCL, then the LIberty, then look for a thread with your sailing date. Each sail will have one long thread, the people on it are your fellow cruisers-to-be. While it takes time to slog through it, you will get lots of information. Even though time is short, you may still find someone with space on a private tour they are organizing, or you may be able to put together a group of "later-comers" like yourself. It's also possible that you'll learn about other recommended tour operators and find a small tour that you can join.