First, recognize that a 4-pin CHA_FANx output connector on your mobo can accept EITHER a 3-pin or a 4-pin case fan. The connectors are arranged so that they only fit one way and make the correct connections no matter which you plug in. You MIGHT need to specify in the BIOS Setup screens that the 4-pin output port is being used for a 3-pin fan, or should NOT use PWM control.
So your problem comes down to finding a power source for the 4th fan. As scartrdfew has suggested, one way is to get an adapter cable and power it from an unused Molex 4-pin output direct from the PSU. That way the fan will run at full speed all the time. You also could get a small fan speed controller module that fits into this line - it is simply a box with a couple of slower-speed settings you can do if you want your fan to run at a slower speed than max.
Another option is to mod two of your fans' wiring. With 3-pin fans, the wires are: Black for Ground, Red for + Vdc, and Yellow for fan speed. When fed from a mobo port that provides fan speed control, the +Vdc pin/line varies from 0 to 12 volts to achieve speed control. The yellow line feeds a fan speed pulse signal (2 pulses per revolution) generated by the fan motor back to the mobo for monitoring. You can snip the connector off the end of one fan's leads and connect its wires to a second fan's thusly: Black to Black, Red to Red, and do NOT connect the loose Yellow to the other one. Just coil it up and tape the end. You don't want to feed duplicate pulse signals from two fans into the mobo. The fan with no yellow wire connection simply will never have its speed signal monitored. AFAIK, most mobo fan ports can provide enough power to run two fans in parallel this way under full mobo control, but I would not try to run more than 2 off one mobo port.
I have seen a few fan adapters that will let you connect 2 3-pin fans together to one mobo port, duplicating the mod I suggested but without requiring you to snip and solder. You may be able to find such a unit. BUT watch out - the ones I saw actually did connect the two yellows together, which I think is wrong.
Thank you, but I got it. The fans came with the adapters, and one of the mobo chans was only like 5v and the rest were 12v so I plugged two fans in to it(one intake and one outtake) and have the other two plugged directly in the psu.