Hello,
I built a home-made set of beach wheels and used a set of rear lawn mower tires. For the hubs, I used aluminum parts from a outdoor handrail supplier. I took two flanges and epoxied 3" PVC and bolted them together. I then made a larger flange out of outdoor plywood which is coated with epoxy and painted. The lug bolts have washers on the back which locks the wooden flange to the aluminum hub. I used a plastic caulking gun tube as the bearing between the hub and the shaft. It's worked great for three years now. I realize that it'll be difficult to come up with the same parts, but maybe you can find something to substitute. Here are some photos.
I can take my wheels apart for easier storage on the trailer.