I should start with stating the fact that you shouldn't be using a carrycot if your child is starting to sit up, it is a safety hazard. Also, a child over 9kg shouldn't be using a bassinet as well. The carrycot harness is not that secure as a seat unit's. I am not trying to be negative, but I am pretty sure you wouldn't want your baby to fall out of your pram, and it, unfortunately, does happen.
Next in line, the adaptors you need are nowhere to be found at this time, I am not sure why. My guess is they are supplying them with the carrycot as that is still available (https://www.babyjogger.eu/en/accesories/city-elite-2-carrycot-346) - I would contact any seller of this, or directly the manufacturer's customer service, asking to be informed if the adaptor set is already included as it is not sold separately.
However, with the Maxi-Cosi-type car seat adapters (like these, click!), you can add not only a car seat (which is probably the better option anyway) but also a few carrycots - e.g., the Cot To Go from Cybex attaches on these adapters. So that is another option to put on a bassinet. (I would still rather use a spacious car seat here, ie. a Maxi-Cosi Cabrio is a large one)
Hope I helped! I mean, it seems to me that the thing you actually need is a reversible-seat stroller. Your baby at 6mo is large enough not to use the carrycot anymore and the car seat is not the comfiest option, usually (if not a reclinable one...). Perhaps your need can actually be covered by at least a temporary reversible model, even a pre-owned second-hand one would do for those few months... Think about it. I wish you all the best.