You probably do NOT need another. I presume the things you want to connect are the MOTOR cables from each of these fans, not the lighting cables. I presume also that the Controller Board included with your case has a connection port and cable that goes to a fan header on the mobo for a control signal.
Most mobos have two (sometimes more) types of fan headers - all very similar, but different in one important detail. All of them use a temperature sensor for guidance because they really alter the fan speed according to a measured TEMPERATURE in a hot item they are cooling. The first group is those used for cooling the CPU chip - includes ones like CPU_FAN, CPU_OPT, AIO_PUMP, etc. All of these use the temp sensor built into the CPU chip itself and should be used for CPU cooling needs only. The second major group are SYS_FAN or CHA_FAN headers that all use a different sensor built into the mobo. These are to be used for all fans that cool the entire case. SOME of these headers may have options to choose a slightly different temp sensor. What you describe above includes THREE fans for your AIO system that cools the CPU, and SEVEN fans that cool the case. So only those latter seven need to be connected to that Controller Board that gets its input signal from a SYS_FAN or CHA_FAN header. You have two 3-from-1 Splitters to handle six fans, plus a third port on the Board for the last fan. The AIO system fans do NOT connect to this Board.
However, of you want a third Splitter anyway, look for a "Fan Splitter", and most likely you'll find hundreds of "4-pin" Splitters. For example, this pair of 2-output Splitters
And this small "board" with five outputs
WATCH OUT! There is another type of device called a HUB for using many fans on one header, and sellers OFTEN mix up the labels they use. A SPLITTER simply connects all its fans in parallel to the output from the host header, so it has only two types of ports. ONE cable goes to the host header to get power and control signals. Then there are two or more outputs to plug in your fans. The ONLY power source for fans on a Splitter is what comes from the host header, and that usually is limited to a max current of 1.0 A, so you need to be sure the load you connect meets that limit. A HUB, on the other hand, has a THIRD connection "arm" that plugs into a power output directly from the PSU so it avoids that Amp limit. BUT a HUB by its design can only be used for the newer 4-pin PWM type of fan - you cannot use it with 3-pin fans. For what you are doing - connecting no more than 3 fans to one fan port - a SPLITTER is quite sufficient. You may note that the Controller Board supplied with your case does have that connection to a SATA power output from the PSU so it is a HUB.
Regarding the fans of the AIO system for CPU cooling, how that is connected and configured usually is detailed in the instructions that came with it. However sometimes there are details that are confusing. Tell us the make and exact model of the AIO system you have, AND the make and model of your MOBO. We can advise precisely how to connect it.
Your list of seven case fans includes one (the pre-mounted rear one) with NO lights, so there are six of them (we presume) with lighting cables to connect somewhere. Moreover, if they all are NZXT fans these connectors are non-standard but DO fit the lighting ports of the Controller Board. So that's where they all go. IF there are lighting cables from the rad fans (and maybe the pump unit) of your AIO system they may need to be connected elsewhere. With the details of the AIO and MOBO as above, we can advise on them, too.