with my idea you can make it yourself if you have a welder. It does look kinda fugly, but the point is it'll be strong as fuck and home-makeable, and you can customize it to whatever size wheel you want on it.
pretty much all you need to make it is:
-a piece of sheet metal (for the middle of the fork, in between the bottom of the tube and and legs, and possibly for the gussets behind the fork legs)
-a tube (1 1/8" OD)
-some square tubing
-a circular saw/table saw (for cutting the square tubing straight to make it look nicer at the bottom of the fork. Not a necessity, so a hacksaw can be used instead.)
-a hole saw (it's basically a blade that attaches onto a drill like a drill bit, you can find one at any hardware store). This is to make a hole in the sheet metal so that the forktube can go in and be welded on both sides to make it stronger.
-a drill with a 5/16" bit
-a 5/16" bolt, and washers,etc. to use as the axle.