The Potentiometer can be found on Amazon for about 8 dollars for2 pcs. even though I only needed one.   The Link to Potentiometer Amazon.com: RioRand DC 3V 6V 12V 24V 35V 5A Motor Speed Controller PWM Speed Control Ultra Small LED Dimmer（2PCS） : Industrial & Scientific

Link to Headers and extension cables.

Cable: Amazon.com: ThreeBulls 5 Pack 4-Pin PWM Fan Splitter Cable, Sleeved Braided Adapter Computer PC Fan Power Extension Cable Converter for Computer ATX Case 4-Pin/3-Pin Cooling Fan Cable (10.6") : Electronics

Headers for PWM Blower Fan connection: PHOENIX CONTACT MKDS 3/4 24AMP, 4 POSTIONS, 400V, Green, Linear Pinning, PCB Terminal Block, Screw Connection with Tension Sleeve, Solder PIN 5MM, Wave Soldering: Amazon.com: Industrial & Scientific

My Setup

I used a 5015 PWM blower fan for the internal filtration, spliced the wires, and connected them to a 2.5pitch 4 pin header ( I used an 8 pin because I had them on hand)  that will clamp down on striped wires from the PWM fan, and plugged the JST extension cable from the PLA port into the headers, and secured it with polyimide tape

The exhaust fan is powered by piggy backing off the PLA port,and tied into the potentiometer for additional control. 

You may have to ream the hole out just a little to get it in perfect, I suggest 5/16 or 8mm bit.   

A short YouTube video of my finished upgrade. Adventure 5M filtration fans. PWM on the PLA port Potentiometer on exhaust. #Adventure5m