that's the bike jimmy was asking me about...
as far as 28" wheels go, you're pretty much out of luck. the original wheels for that bike were probably "wood clad," meaning the were made out of wood and covered in a thin sheet of tin. built way before metal extruding machines were invented. or they might've been completely made outta wood.
28's are a rare size today, with 700c being the closest equivalent, and to my knowledge, they only make that size in skinny roadbike rims.
there are 29'rs now, but those might be too big. but getting a fork from a 29" bike might be the way to go, but you'll still need to check the clearance in the rear.
any wheel can be laced up to any hub, providing they have the same spoke count. correct length spokes may be hard to find. with your situation you might find that afyer you go through all the trouble getting the parts, they don't fit into your frame.
i built a 1920's Colson Flyer that had 28's originally, using 26" alloy cruiser wheels, and had to use skinnier tires that still barely cleared in the rear.
using the original fork, there wasn't much of a noticeable gap with the smaller diameter wheels, but i had to modify 26" fenders to space it all out.
it's the black and orange bike with a copper tank in my albums. there's a thread here somewhere. search "colson flyer" and you should find it.
original iver johnson parts show up on ebay, but they ain't cheap.
good luck.