The first thing to do is find a BMX front fork with a about 1.3 inches of rake or more. Then add and extension using an angle bar to hold it in place. You can buy threaded steer tube if you don’t want to use a thread-less head set. Cut the threads to fit the stack height.
But if you need a disc brake on the front, it would be much easier to buy a Recumbent bike disc fork off eBay and insert an extension. Better to use a rim brake for emergency only on the front, and use a really good disc brake on the rear. Hydraulic if your going to haul really heavy cargo down steep hills!
Steer tube 1 inch OD x .834” ID x .083” wall (use thread less headsets or buy a threaded steer tube )
Head tube 1- 3/8th OD x 1.185” ID x .095” wall
Steer tube 1- 1/8th inch OD x .955” ID x .095” wall
Head tube 1-1/2” OD x 1.334” ID x .083” wall