I made a few by using fork crowns (Pacenti MTB one in particular) and cutting the blades off of pre-made 26” or 700c forks to get pre-raked blades with intact dropouts. It takes out most of the work of making a fork, and the typical 45mm rake works well for the low trail handling that I like on cargo bikes.
I made long (500mm) steerers by using 9/8 by 058 tubing and turning a thicker piece into a tapered butt that could be inserted into the bottom.
I can’t guarantee results or safety, but this worked well for me. One of those forks is almost 20 years old and has plenty of cycle truck miles.
another option is to get a normal 20in fork and extend the steerer.
I have extended steerers before and it’s not hard at all. That would be what I do next if I ever build another minivelo.
Thank you! Your comment sent me down the rabbit hole and I found out that BFS also has 420 and 450 options in stock! Not sure how I missed them but order is in!
Might be worth it to reach out to bike Friday and see if you can buy an all packa fork. Their most recent version is boost and thru axle and the previous two are 100m QR
